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THE ELEMEIsTTS 



J2, / <?" 

PHYSIOLOGY AND HYGIENE; 



A TEXT-BOOK 



FOR EDUCATIONAL INSTITUTIONS, 



BT 

THOS. H. HUXLEY, LL.D., F. R. S., 

AND 

WM. JAY youma:n"s, m. d. 

WITH NUMEROUS ILLUSTRATIONS. 



NEW YORK : 

D. APPLETON AND COMPANY, 
443 & 445 BROADWAY. 

18G8. 






74952 



Entered, according to Act of Congress, in the year 1868, by 

D. APPLETON & CO., 

In the Clerk's Office of the District Court of the United States for the 

Southern District of New York. 




'/ 



PEEFACE. 



A FEW words are necessary to explain tlie joint authorship 
of the present volume. 

My friend and teacher, Professor Huxley, having been for 
a considei-able time engaged in the preparation of an element- 
ary work on Physiology, at such brief intervals as he could 
snatch from his laborious scientific researches, and it having 
been suggested to him that its republication in this countiy 
might be desirable, he confided the early sheets of the work to 
me, to make such additions of matter and modifications of 
form as might be thought proper to adapt it to the circum- 
stances and requirements of American education. This I have 
done to the best of my judgment by contributing eight chap- 
ters to the present edition: the first, on the relation of Physiol- 
ogy to the other sciences; and the last seven, forming Part IL, 
which treats brieiiy of general Hygiene, or the application of 
the principles of Physiology to the art of preserving health. I 
have also numbered the paragraphs of the work continuously, 
prefixed headings to them, and appended a set of questions to 
the whole. 

His aim in the preparation of the Physiology, and its lead- 



IV PREFACE. 

ing and most important characteristics, are thus described by 
Prof. Huxley : 

"My object in writing it has been to set down, in plain 
and concise language, that which any person who desires to 
become acquainted with the principles of Human Physiology 
may learn, with a fair prospect of having but little to unlearn 
as our knowledge widens. 

" It is only by inadvertence, or from an error in judgment, 
therefore, that the work contains any statement, or doctrine, 
which cannot be regarded as the common property of all 
physiologists. I have endeavored simply to play the part 
of a sieve, and to separate the well-established and the essen- 
tial from the doubtful and the unimportant portions of the 
vast mass of knov/ledge and opinion we call Human Phys- 
iology." 

That there was imminent need of the perfonnance of this 
task by some able hand, a critical examination of our popular 
text-books of Physiology will abundantly attest. But it is 
not to be inferred that this has been done by merely collating 
old views which have long passed current, and neglecting the 
results of the most recent inquiry. In true science, the essen- 
tial progress of which consists in the rigorous sifting and veri- 
fication of opinions, the latest knowledge is ever the clearest 
and the ripest. It will therefore be found that, while Prof. 
Huxley's work inexorably winnows away the chaff of discred- 
ited doctrine and doubtful speculation, it nevertheless em- 
bodies the valid and established results of the latest investiga- 
tions, and may therefore be accepted as a brief exposition of 
the actual present state of knowledge upon the subject. 

Probably, the most important advance which has been 
lately made in the field of science consists in the establish- 



PREFACE. V 

ment of the great principle of the correlation and conserva- 
tion of forces. Accordingly, regarding Physiology as strictly 
the science of vital actions or living forces, Prof. Huxley 
tacitly conforms the whole plan of his work to this funda- 
mental principle. Committing himself to no unsettled theo- 
ries respecting the transformations of energy, he neverthe- 
less views the living organism dynamically^ as a problem of 
the disturbance and restoration of equilibrium between the 
receipt and expenditure of matter and force. The functions 
of alimentation, circulation, respiration, and secretion, and the 
exercise of physical and mental power, are considered in the 
light of losses and gains to the system, and with constant 
reference to the physiological balance of forces. 

Another marked and important feature of Prof. Huxley's 
work is the style in which it is written. AVith plainness and 
concision of language he has attained an admirable compres- 
sion of statement by Avhich a large body of facts and principles 
is brought within the narrowest compass of lucid presentation. 
Wliile excessive simplification and expansion of style may be 
suited to scientific works designed for merely popular reading, 
the case is different with a class-room manual intended for syste- 
matic study. Here the object is not only to inform the under- 
standing, but to call out and discipline the powers of the mind 
through continuous eftorts of thought. Prof. Huxley's elemen- 
tary treatise, while it embodies an amount of physiological 
science such as every educated person ought to possess, will also 
be found in its concentration of thought and compactness of ex- 
pression well adapted for the higher purposes of mental culture. 

My own additions to the volume have been made in 
response to a growing demand that the subject of Hygiene, 
in both its bodily and mental aspects, shall receive increasinor 



VI PEEFACE. 

attention in general education. I trust that the acknowledged 
importance of this subject, as well as the advantage of dealing 
with it separately, after the Physiology has been mastered, 
will in some degree promote the favi^rable reception of the 
work by the teachers of the country. 

I take this occasion to express thanks to my brother, Dr. 
E. L. Youmans, for superintending the passage of the work 
through the press, and for various important suggestions ; and 
also to Dr. Wm. A. Hammond, of New York, for having 
kindly read the proofs of the closing chapter on Mental 
Hygiene. 

W. J. Y. 

State Normal School, Winona, Minn., 
October, 1867. 



OOI^TENTS. 



PAET I. 

ELEMENTARY PHYSIOLOGY. 



CHAPTER I. 

PAGE 

Relations of Physiology to other Branches of Science, . 11 

Sect. 1. — Nature of Scientific Knowledge, . . . .11 

2. — The Preparatory Sciences, .... 13 

8. — The Biological Sciences, 14 

CHAPTER II. 
A General View of the Structure and Functions of the Hu- 
man Body, . 19 

Sect. 1. — Work and Waste, 20 

2. — Outlines of the Bodily Structures, ... 23 

3.— The Bodily Tissues, 26 

4. — The Combination of Actions, .... 29 
5. — Nutrition, Circulation, Excretion, . . . .82 

CHAPTER III. 
The Vascular System and the Circulation, . . . . 35 

Sect. 1. — The Vascular System, 35 

2. — Connections and Structure of the Heart, . . 44 

8. — Working of the Heart and Vessels, . . .52 
4. — The General Circulation, 59 

CHAPTER IV. 

Of the Blood and Lymph, 65 

Sect. 1. — Its Microscopical Elements, .... 65 

2. — Its Physical and Chemical Properties, . . .72 



VIU 



CONTENTS. 
CHAPTER V. 



Of Kespiration, 

Sect. 1. — Arterial and Yenous Blood, . 
2.— The Lungs and their Office, 
3.— The Respiratory Mechanism, 
4. — Inspiration and Expiration, 
5. — Effects of Respiration, 

CHAPTER YL 

The Sources of Loss and of Gain to the Blood, 
Sect. 1. — Sources of Loss to the Blood, 
2. — Losses and Gains by the Liver, 
3. — Sources of Gain to the Blood, 

CHAPTER Vn. 
The Function of Alimentation, .... 
Sect. 1.-— Properties of Food-Stufis, . 
2. — Preliminaries of Digestion, 
3. — Stomach-Digestion, 
4. — Intestinal-Digestion, 

CHAPTER Yin. 

Motion and Locomotion, 

Sect. 1. — Instruments of Motion, 

2. — Mechanism of Bodily Movements, 
3. — Movements of Locomotion, 
4. — Yocal Movements, . . 

CHAPTER IX. 
Of Sensations and Sensory Organs, .... 
Sect. 1. — Reflex Action — Groups of Sensations, 
2.— Touch, Taste, and Smell, . 
3. — The Mechanism of Hearing, . 
4. — Working of the Auditory Mechanism, 



CHAPTER X. 



The Organ of Sight, 



Sect. 1. — Structure and Action of the Retina, 
2. — The Luminous Agent, . 
3. — The Intermediate Apparatus, . 
4 — Focal Adjustment, 
5. — Appendages of the Eyeball, 



PAGE 

81 
81 
84 
90 
95 
100 



106 
106 
120 
124 



133 
133 
340 
145 

148 



153 
153 
156 

168 

no 



111 
111 

180 
188 
196 



201 
201 

207 
209 
211 
216 



CONTENTS. IX 

CHAPTER XL 

PAGE 

Sensations and Judgment, 219 

Sect. 1. — Compound Sensations, 219 

2. — Delusions of Judgment, ..... 222 

3. — Visual Sensations and Mental States, . . . 229 

CHAPTER XII. 

The Nervous System and Innervation, 236 

Sect. 1.— The Spinal Cord— Reflex Action, . . . .236 

2.— The Brain, 245 

3. — The Cerebral Nerves, 249 

4. — Unconscious Cerebration, 252 

CHAPTER XIII. 
Histology ; or, the Minute Structure of the Tissues, . .255 

Sect. 1.— Dermal Tissues, 255 

2. — Interior Tissues, 260 

3.— Osseous Tissues, ...... 263 

4. — Muscular and Nervous Tissues, .... 270 



PART II. 

ELEMENTARY HYGIENE, 



CHAPTER XIY. 

Scope and Aims op Hygiene, .... . . 2'75 

CHAPTER X7. 

Air and Health, 282 

Sect. 1. — Impurities of the Air, 282 

2.— Morbid Effects of Impure Air, . . . .287 

3.— Purification of the Air, 291 

CHAPTER XYI. 

Water and Health, 296 

Sect. 1.— Physiological Office of Water, . . . . 296 

2.— Different Kinds of Water, 297 

3. — Morbid Eflfects of Impure Water, . . . 302 

4. — Purification of Water, 806 



X CONTENTS. 

CHAPTER XYII. 

PAGE 

Food and Health, 308 

Sect. 1. — The Alimentary Principles of Food, . . . 308 

2.— Animal Foods, 312 

3.— Vegetable Food, 315 

4. — ^Auxiliary Foods, 318 

6. — Culinary Preparation of Foods, . . . 324 

6.— Injurious Effects of Bad Diet, .... 326 

CHAPTER XVIII. 

Clothing and Health, . 334 

Sect. 1. — Properties of Clothing Material, . . . 334 

2. — Manner of Dressing the Body, .... 337 

CHAPTER XIX. 

Exercise and Health, 344 

Sect. 1. — Labor and Exercise, 344 

2. — Effects of Regulated Exercise, . . . . 345 

3. — Excessive and Insufficient Exercise, . . . 349 

CHAPTER XX. 

Mental Hygiene, 353 

Sect. 1.— Relations of Mind and Body, .... 353 

2. — Forms of Mental Impairment, .... 357 
3. — Causes of Mental Impairment, . . . .375 



PAET I. 
ELEMENTARY PHYSIOLOGY. 



CHAPTER I 

EELATIONS OF PHYSIOLOGY TO OTHER BRANCHES OF SCIENCE. 

INTRODUCTORY. 

Section I. — Nature of Scientific Knowledge, 

1. How it Originates. — ^Physiology is one of the branches 
of Science, and we cannot better commence its study than by 
forming clear ideas of the general nature of science itself, and 
of the relations which this branch of it bears to its other parts. 
By mapping out the family of Sciences to which Physiology 
belongs, and upon which it depends, we may get a definite 
conception of its position and relations in the group : to this 
the present chapter will be devoted. 

Man has been called the Interpreter of Nature, and Science 
defined as its right interpretation. But the true interpretation 
of Nature is a slow and difficult work. There is a curiosity in 
the human mind to seek explanations and understand the rea- 
sons and causes of things ; but at first its questions are put at 
random and answered vaguely, and knowledge is then rude and 
imperfect. With increasing experience questions are put more 
sharply and go deeper, and then come clearer explanations and 
a better understanding of things. In this way knowledge upou 



12 ELEMENTARY PHYSIOLOGY. 

Tnany subjects grows to be more and more perfect ; and when 
it becomes so accurate and sure that it is capable of being 
proved to persons of suitable intelligence, it is called science. 
The science of any subject is the highest and most exact 
knowledge upon that subject. 

2. The Order of Nature. — That which makes science pos- 
sible is the regularity of Nature's order, and it is only possible 
so far as that order can be traced. All the appearances and 
effects of Nature with which we can become acquainted are 
known as Phenomena ; those which exist together constitute 
the order of Coexistences ; those which follow each other in a 
regular succession form the order of Sequences. Thus all the 
various parts of the human body, as bones, blood-vessels, 
nerves, and fluids, and its simultaneous operations, as of breath- 
ing, digestion, circulation, constitute its coexistences ; while the 
succession of its numerous actions and effects, as for example the 
agreeable feeling and renewed strength which follow the taking 
of food, constitutes its sequences. A scientific inquiry into the 
order of Nature, therefore, resolves itself into an investigation of 
the relations of coexistence and sequence among all objects, while 
each science is a statement of the coexistences and sequences 
of some particular part of Nature. If there are any subjects 
which have no coexistences and no sequences ascertainable 
by the human mind, those subjects are incapable of becoming 
sciences. 

3. Connection of the Sciences. — Science is thus the most 
perfect knowledge of Nature in all her aspects. But the parts 
of Nature are intimately connected in one great whole ; there- 
fore the sciences which give an account of Nature must also be 
intimately connected together. They overlap and interlace in 
the closest manner, so as to be in a very great degree mutually 
dependent on each other. To understand any one of them, it 
is therefore important to have some knowledge of the others 
most nearly related to it, and upon which it essentially de- 
pends. 



THE PREPAKATORY SCIENCES. 13 



Section II. — The Preparatory Sciences, 

4. Mathematics. — The least dependent of all the sciences, 
and at the same time the simplest and the easiest, is that which 
considers the number and the forms, or shapes of objects, and 
this is Mathematics, or the science of quantity. We cannot 
think of things except as having form or outline, and the 
science which deals with forms and their relations is termed 
Geometry; nor can we think of them except as one or many — 
that is, as being numbered, and a knowledge of the combina- 
tions and relations of numbers constitutes the science of Arith- 
metic, So simple, clear, and definite are these ideas that they 
may actually be considered apart from the things to which they 
apply, so that arithmetic can deal, as it were, with pure num- 
bers rather than with things numbered, and geometry with 
space rather than the objects contained in space. The ideas 
may be thus abstracted from the realities, hence mathematics is 
known as the most abstract of the sciences ; and as the ideas 
with which it deals are few, it has been carried to the highest 
perfection of any science. 

As in all other sciences we have constantly to use mathe- 
matical ideas, a certain amount of elementary arithmetic and 
geometry is useful and important as a preparation for this kind 
of study. 

5. Physics. — The science which comes next is that which 
passes to the actual study of things ; which goes from ideas of 
number to those of the objects numbered ; from the notion of 
space to that which occupies space, or which adds to mathe- 
matical conceptions those of matter and force. It considers 
the universal and essential properties of matter, the forces 
which act on it to produce motion, and the resulting laws of 
motion. This branch of science is called Physics or Natural 
Philosophy, and treats of the resistance, weights, pressures, 
mutual attractions, and general properties of material bodies. 
It is not so simple as mathematics, yet the conceptions with 



14 ELEMENTARY PHYSIOLOGY. 

which it deals are so few that it has been worked out to a con- 
siderable degree of perfection. 

6. Chemistry. — If there were only one kind of matter in 
the universe, as iron or sulphur, there could still be a science of 
physics. But there is a large number of elementary bodies in 
Nature which combine intimately together in various propor- 
tions and give rise to that infinite diversity of material sub- 
stances which we see around us. These all have the general 
physical properties, but they have also certain special and pecu- 
liar properties which are different in different kinds of matter. 
The knowledge of these gives rise to the science of chemistry, 
which treats of substances as simple or compound, how they 
are constituted, and how they act upon and change each other. 
But a knowledge of the universal and constant properties of 
bodies should precede the study of the more special and vari- 
able properties ; hence physics prepares for chemistry. The 
ideas which pertain to chemistry are far more numerous and 
complex than those of physics, and accordingly chemistry is 
much more backward than physics in its development. 

Section III. — The Biological Sciences, 

7. Biology. — ^All the objects of Nature may be divided into 
two great classes — the living or the organic, and the not-living 
or the inorganic. Biology is the name of that comprehensive 
science which treats of living matter and living things in all 
their grades, forms, and varieties. But in entering the field of 
biology we do not begin anew ; we carry with us a stock of 
mathematical, physical, and chemical conceptions. We have 
still to deal with numbers and forms, with the motion and rest 
of masses, and with the composition and internal changes of 
substances. These are indispensable keys to biological phe- 
nomena, and not an intelligent step can be taken without them ; 
but there is also a new order of ideas which is peculiar to this 
great field of thought, as those of organic structure, vital func- 
tion, growth, development, waste and repair, alimentation, 



THE BIOLOGICAL SCIENCES. 15 

reproduction, &c. Biological subjects are therefore far more 
difficult to investigate, and are incapable of the exactness 
which belongs to the inorganic sciences ; still they comprise a 
great body of certain and most valuable knowledge. 

8. Divisions of Biology. — The first division of Biology is 
that which everybody recognizes — the division into plants and 
animals, which gives rise to the two sciences of Botany and 
Zoology, But while this division is most obvious and 
natural, it does not answer the full purpose of scientific classifi- 
cation, which aims to group together all phenomena of the 
same kind, thus avoiding repetition in their treatment. Every 
living being, whether plant or animal, presents the same series 
of questions for consideration ; vegetable-biology would there- 
fore be simply going over again the inquiries of animal-biology. 
These inquiries may be arranged into four groups, giving rise 
to four fundamental divisions of biological science. 

9. Morphology. — This word, in its derivation, signifies the 
doctrine of forms. Applied to the organic world it is that 
division of Biology which treats of the forms or structures of 
living beings. It has several branches. For example, no living 
being is throughout of homogeneous substance ; the most of 
them are highly complex, from the union of many dissimilar parts. 
The statement of this structure constitutes Anatomy^ and if it 
is carried down to the minutest microscopical elements of the 
organism, it is known as Histology, 

Again, no living being retains the same form and size 
throughout the course of its existence, but all grow, or pass 
through a series of changes, sometimes simple, sometimes very 
complicated, and the statement of these changes of form consti- 
tutes the branch of Morphology termed Development. 

Furthermore, when the structure and development of any 
number of plants or animals have been ascertained, the question 
then arises of their resemblances and difterences. Thus the 
panther and the cat are more like each other than either is like 
the dog ; but they and the dog are more like each other than 
either is like the sheep ; while sheep, dog, and cat resemble 



16 ELEMENTARY PHYSIOLOGY. 

each other more than either does a fowl. In this way plants 
and animals which resemble each other in internal and external 
.characters are arranged into groups to which a common name 
is applied, and this is Classification, The rude divisions of the 
vegetable world into trees, shrubs, and plants, and of the ani- 
mal world into beasts, birds, and creeping-things, science car- 
ries out in a precise and accurate manner for all the races of 
living beings. Classification depends upon anatomy and de- 
velopment, and is grounded upon the facts which they have 
established, and the fulness v/ith w^hich this is done indicates 
the completeness of the science of Morphology. 

10. Distribution. — This is the second great division of 
Biology. Very few plants or animals are found all over the 
world ; most of them are restricted to limited areas of the 
earth's surface. Of terrestrial animals and plants, some are 
found only at particular elevations ; while of aquatic creatures, 
some are found only at certain depths. Again, great numbers 
of animals and plants have existed in former periods of the 
earth's history Avhich do not now exist, and we get a knowl- 
edge of them through their fossil relics. The definition of the 
range of any plant or animal under any of these conditions — 
its location in space or in time — which leads to the knowledge 
of its environing circumstances, is its Distribution, 

11. Physiology. — If we suppose an animal dead and petri- 
fied, its study might still give rise to all the branches of science 
hitherto enumerated. Not only Avould it exemplify the laws 
of quantity, physical properties, and a chemical constitution, 
but also all the branches of Morphology. Its structure or 
anatomy could be determined, its relations to other living be- 
ings, or its place in classification, and its position in space and 
in time, that is, its relations to surrounding nature, or its distri- 
bution. But when we conceive of it as alive, in motion, and 
undergoing changes, a new order of phenomena and a new set 
of inquiries are presented, w^hich give rise to the science of 
Physiology, the third great branch of Biology. 

Every living being does certain things, performs certain 



THE BIOLOGICAL SCIENCES. 17 

actions which are called functions^ and is so far to be regarded 
as a machine working toward a given end. Physiology, there- 
fore, considers the living being as a machine in action^ and in- 
quires into the uses, operations, and mutual influence of its 
parts and the conditions under which its activity is maintained. 
Dealing with force or power, it considers living organisms under 
their dynamical aspects as Morphology regards them in their 
statical aspects. 

Physiology is divided into animal and vegetable physiology, 
and animal physiology is again divided into Comparative Phy- 
siology^ which treats of the inferior races, and Human Physiol- 
ogy^ which considers the physiological phenomena of man. 
Because many of the inferior creatures have a simpler consti- 
tution, and are more accessible for purposes of investigation, 
the study of comparative physiology has been a great help 
to the advance of human physiology, and some knowledge of 
the former is of much value in prosecuting the latter. 

12. Etiology. — Physiology treats of power, of which we 
know nothing except in its results. It involves the idea of 
causes producing effects, and is therefore a causal science. 
Morphology says that in such-and-such circumstances the living 
being is structured so-and-so. These are effects, and how pro- 
duced it is the business of physiological research, as far as 
possible, to explain. The physiology of individual life thus 
expands into a broad inquiry concerning the causes of vital 
phenomena in general, and the limits within which living beings 
can be affected by external conditions. This more compre- 
hensive physiology is termed Etiology, which literally signifies 
the doctrine of causes, and forms a fourth branch of biological 
science. The laws of the variations of living beings, of the 
modifications of individual organisms and successions of organ- 
isms, and of the influence of physical agencies on their posi- 
tion in space or their persistence in time, or the " dynamics of 
distribution," as it has been called, belong to this division of 
the general subject. It is the most complicated and least per- 
fect of all the branches of Biology. 



18 ELEMENTARY PHYSIOLOGY. 

13. Claims of Physiological Study. — There are two classes 
of reasons why Physiology should be well studied by all who 
aspire to be in any tolerable degree educated. The first is, that 
it is a part^ and a most important part, of the great order of 
Nature which the human mind is adapted to miderstand. The 
first duty of a rational being is to cultivate in the best manner 
possible the higher powers of his nature, and in no w^ay can 
this be done so w^ell as by studying the plan of Nature, which 
is full of harmony, beauty, and the highest instruction. Thou- 
sands of the greatest minds that have appeared in the world 
have been occupied for ages in discovering the truths of Nature, 
and a large amount of the most valuable and interesting knowl- 
edge has thus been reached, of which past generations knew 
little, and the acquisition of which is the noble privilege of the 
present time. Is it right that all this vast research which has 
employed the genius of ages should go for nothing in education 
— that all this wealth of knowledge should be passed by as if it 
had no existence, and the young people of this country grow 
up as ignorant of it as if they had lived a dozen centuries ago ? 

14. Applied Physiology— Hygiene. — Another and an im- 
perative reason for studying Physiology is, that it opens to us a 
true understanding of our own natures. It teaches us how to 
take care of ourselves, to preserve health, to economize strength, 
and to improve and invigorate all our faculties. A large 
amount of the suff'ering of life comes from self-exposure and 
self-abuse, which take numberless forms. These may be avoid- 
ed through proper knowledge conscientiously applied. Tlie 
truths of Physiology should therefore be inculcated and en- 
forced early and earnestly, and with the emphasis of high reli- 
gious duty. 

Physiology treats of the laws of the human constitution in 
a state of health ; but so important is the application of physio- 
logical principles to the art of preserving heahh and preventing 
disease, that a second part has been added to the present work, 
treating definitely and separately of this application, the princi- 
ples and rules of which constitute the art of Hygiene. 



THE BIOLOGICAL SCIENCES. 19 

\ 



'\ ^^ 



CHAPTER II. 



A GENERAL VIEW OF THE STRUCTUPwE AND FUNCTIONS OF 
THE HUMAN BODY. 

15. How bodily Actions are Studied.— The body of a liv- 
ing man performs a great diversity of actions, some of wbicli 
are quite obvious; others require more or less careful obser- 
vation ; and yet others can only be detected by the employ- 
ment of the most delicate appliances of science. 

Thus, some part of the body of a living man is plainly 
always in motion. Even in sleep, when the limbs, head, and 
eyelids may be still, the incessant rise and fall of the chest con- 
tinue to remind us that we are viewing slumber and not death. 

But a little more careful observation is needed to detect the 
motion of the heart ; or the pulsation of the arteries ; or the 
changes in the size of the pupil of the eye with varying light; 
or to ascertain that the air which is breathed out of the body 
is hotter and damper than the air which is taken in by 
breathing. 

And lastly, when we try to ascertain what happens in the 
eye when that organ is adjusted to different distances ; or what 
in a nerve when it is excited ; or of what materials flesh and 
blood are made ; or in virtue of what mechanism it is that a 
sudden pain makes one start — we have to call into operation all 
the methods of inductive and deductive logic ; all the resources 
of physics and chemistry ; and all the delicacies of the art of 
experiment. 

16. Scope of Human Physiology. — The sum of the facts 
and generalizations at which we arrive by these various modes 
of inquiry, be they simple or be they refined, concerning the 
actions of the body and the manner in which those actions are 
brought about, constitutes the science of Human rhysiology. 
An elementary outline of this science, and of so much anatomy 
as is incidentally necessary, is the subject of the following 



20 ELEMENTARY PHYSIOLOGY. 

chapters, of which I shall devote the present to an account of 
so much of the structure and such of the actions (or, as they 
are technically called, " functions ") of the body, as can be 
ascertained by easy observation, or might be so ascertained 
if the bodies of men were as easily procured, examined, and 
subjected to experiment as those of animals. 

Section I. — TFork and Waste. 

17. Bodily Loss or Expenditure. — Suppose a chamber 
with walls of ice, through which a current of pure ice-cold air 
passes, the walls of the chamber will of course remain un- 
melted. 

Now, having weighed a healthy living man with great care, 
let hmi walk up and down the chamber for an hour. In doing 
this he w411 obviously exercise a great amount of mechanical 
force, as much, in fact, as would be required to lift and push 
his weio;ht throuo-h the distance which he has raised himself at 
every step, and transported himself by all his steps. But, in 
addition, a certain quantity of the ice will be melted or con- 
verted into water, showing that the man has given off heat in 
abundance. Furthermore, if the air which enters the chamber 
be made to pass through lime-water, it wdll cause no cloudy 
white precipitate of carbonate of lime, because the quantity of 
carbonic acid in ordinary air is so small as to be inappreciable 
in this way. But if the air which passes out is made to take 
the same course, the lime-water will soon become milky, from 
the precipitation of carbonate of lime, showing the presence 
of carbonic acid, which, like the heat, is given off by the man. 

Furthermore, even if the air be quite dry as it enters the 
chamber, that which is breathed out of the man, and that w^hich 
is given off from his skin, will exhibit clouds of vapor, wdiich 
vapor, therefore, is derived from the body. 

After this experiment has continued for a longer or a short- 
er time, let the man be released and weighed once more. He 
will be found to have lost weight. 



WORK AISTD WASTE. 21 

Thus a living, active man constantly exerts mechanical force^ 
gives off heat^ evolves carbonic acid and water^ and undergoes a 
loss of substance, 

18. A Physiological Income indispensable. — Plainly, this 
state of things could not continue for an unlimited period, or 
the man would dwindle to nothing. But long before the effects 
of this gradual diminution of substance become apparent, they 
are felt by the subject of the experiment in the form of the two 
imperious sensations called hunger and thirst. To still these 
cravings, to restore the weight of the body to its former amount, 
to enable it to continue giving out heat and water and carbonic 
acid at the same rate for an indefinite period, it is absolutely 
necessary that the body should be supplied with each of three 
things and with three only. These are, firstly, fresh air; 
secondly, drink, consisting of water in some shape or other, 
however much it may be adulterated ; thirdly, food, in which that 
compound known to chemists as protein^ and containing carbon, 
hydrogen, oxygen, and nitrogen, must be contained if it is to 
sustain life indefinitely ; and in which fatty and starchy or sac- 
charine matters ought to be contained, if it is to sustain life 
conveniently. 

19. Forms of Excretions. — Of this food a certain small 
proportion of useless and indigestible material leaves the body 
in the condition in which it entered it, and without ever being 
incorporated with its substance, as excrementitious matter. 
But, under healthy conditions, and with only so much food as 
is necessary, no important proportion of either protein matter, 
or fat, or amylaceous, or saccharine food leaves the body by 
this or any other channel. Almost every thing that leaves the 
body, in fact, does so either in the form of loater, or of carbonic 
acid, or of a third substance called zura, and of certain com- 
paratively unimportant saline compounds. 

20. Absorption of Oxygen. — Chemists liave dctennined 
that these products which leave the body and are called cvcrc- 
tions, contain, if taken altogether, far more oxygen than the 
food and water taken into the body. Now, the only possible 



22 ELEMENTARY PHYSIOLOGY. 

source whence the body can obtain oxygen, except from food 
and water, is the air which surrounds it. And careful investi- 
gation of the air Avhich leaves the chamber in the imaginary 
experiment described above, would show, not only that it has 
gained carbonic acid from the man, but that it has lost oxygen 
in equal or rather greater amount to him. 

21. Variation of the Physiological Balance.— Thus, if a 
man is neither gaining nor losing weight, the sum of the 
weights of all the substances above enumerated which leave 
the body, ought to be exactly equal to the weight of the food 
and water which enter it, together with that of the oxygen 
which it absorbs from the air. And this is proved to be the case. 

Hence it follows that a man, in health, and ** neither gain- 
ing nor losing flesh," is incessantly oxidating and wasting away 
and periodically making good the loss. So that if he could be 
confined in the scale-pan of a delicate spring balance, like that 
used for weighing letters, in his average condition, the scale- 
pan would descend at every meal and ascend in the intervals, 
oscillating to equal distances on each side of the average posi- 
tion, which would never be retained for longer than a few 
minutes. There is, therefore, no such thing as a stationary 
condition, and what we call such is simply a condition of varia- 
tion within narrow limits — a condition in which the gains and 
losses of the numerous daily transactions of the economy bal- 
ance one another. 

22. Conditions of this Balance. — Suppose this condition 
of daily physiological balance to be reached, it can be main- 
tained only under the condition that the quantity of the me- 
chanical work done, or of heat or other force evolved, remains 
absolutely stationary. 

Let such a physiologically balanced man lift a heavy body 
from the ground, and his previous loss of weight will be imme- 
diately increased by a definite amount, which cannot be made 
good unless a proportionate amount of extra food be supplied 
to him. Let the temperature of the air fall, and the same re- 
sult will occur, if his body remains as warm as before. 



WOKK AND WASTE. 23 

On the other hand, diminish his exertion and lower his pro- 
duction of heat, and either he will gain weight or some of his 
food will remain unused. 

23. Equation of Food and Force. — Thus, in a properly 
nourished man, a stream of food is constantly entering the body 
in the shape of complex compounds containing comparatively 
little oxygen ; as constantly, the elements of the food are leav- 
ing the body, combined with more oxygen. And the incessant 
breaking down and oxidation of the complex compounds which 
enter the body is definitely proportioned to the amount of force 
the body exerts, whether in the shape of heat or otherwise : 
just in the same way as the amount of work to be got out of a 
steam-engine, and the amount of heat it and its furnace give 
oil*, bear a strict proportion to its consumption of fuel. 

Section II. — Outlines of the Bodily Structure, 

24. Structure of the Vital Mechanism. — From these gen- 
eral considerations regarding the nature of life, considered as 
physiological work, we may turn for the purpose of taking a 
like broad survey of the apparatus which does the work. We 
have seen the general performance of the engine, we may now 
look at its build. 

The human body is obviously separable into head, trunk, 
and limbs. In the head, the brain-case, or skull, is distinguish- 
able from the face. The trunk is naturally divided into the 
chest or thorax, and the abdomen or belly. Of the limbs there 
are two pairs — the upper, or arms, and the lower, or legs; 
and legs and arms again are subdivided by their joints into 
parts which obviously exhibit a rough correspondence — thigh 
and arm, leg and forearm, ankle and w^rist, fingers and toes, 
plainly answering to one another. And the last two, in fact, 
are so similar that they receive the same name of ^' digits ; '' 
while the several joints of the fingers and toes have the com- 
mon denomination of " phalanges." 

The whole body thus composed is seen to be bilaterally 
symmetrical ; that is to say, if it were split lengthways by a 



24 ELEMENTARY PHYSIOLOGY. 

groat knife, whicli should be made to pass along the middle 
line of both the dorsal and ventral (or back and front) aspects, 
the two halves would almost exactly resemble one another. 

25. The Vertebral Column. — The bisected aspect of one- 
half of the body, divided in the manner described (Fig. 1), 
would exhibit, in the trunk, the cut faces of thirty-three bones, 
joined together by a very strong and tough substance into a 
long column, which lies much nearer the dorsal than the ven- 
tral aspect of the body. The bones thus cut through are called 
the bodies of the vertebrse. They separate a long, narrow 
canal, called the spinal canal, which is placed upon their dorsal 
side, from the spacious cavity of the chest and abdomen, which 
is lodged upon their ventral side. There is no direct commu- 
nication between these two cavities. 

26. Internal Organs. — The spinal canal contains a long 
white cord — ^the spinal cord — which is an important part of 
the nervous system. The ventral chamber is divided into the 
two subordinate cavities of the thorax and abdomen by a re- 
markable partition, the diaphragm (Fig. 1, Z>), which is con- 
cave toward the abdomen, and convex toward the thorax. The 
alimentary canal (Fig. 1, AL) traverses these cavities from one 
end to the other, piercing the diaphragm. So does a long double 
series of distinct masses of nervous substances, which are called 
ganglia, are connected together by cords, and constitute the so- 
called " sympathetic " (Fig. 1, xSy.). The abdomen contains, in 
addition to these two sets of organs, the two kidneys, one placed 
against each side of the vertebral column, the liver, the pan- 
creas, or " sweet-bread," and the spleen. The thorax encloses, 
besides its segment of the alimentary and sympathetic canal, 
the heart in the middle, and the two lungs, one on each side. 

27. The Head and Brain. — Where the body is succeeded 
by the head, the uppermost of the thirty-three vertebral bod- 
ies is followed by a continuous mass of bone, which extends 
through the whole length of the head, and, like the spinal 
column, separates a dorsal chamber from a ventral one. The 
dorsal chamber, or cavity of the skull, opens into the spinal 



OUTLINES OF THE BODILY STRUCTURE. 



25 



canal, and contains a mass of nervous matter called the brain, 
which is continuous with the spinal cord, the brain and the 
spinal chord together constituting what is termed the cerebro- 
spinal axis [C.S.J C.S,), 

The ventral chamber, or cavity of the face, is almost en- 
tirely occupied by the pharynx and mouth, which are the 
upper expanded terminations of the alimentary canal. 

28. The Human Body a Double Tube.— Thus the study of 




Fig. 8. 



Fig. 1, a diasTnmmatic section of the human body, taken vertically through the 
median plane. C.S. the cerebro-spinal nervous system ; N the cuvity of tbe nose ; JLf 
that of the mouth; Al., Al. the alimentary canal represented as a simple straight 
tube; //the heart; D the diaphrajjm ; Sif. the sympathetic gandia. 

Fig. 2, a transverse vertical section of the head taken parallel with the line ah; 
letters as before. 

^'i^. 3, a transverse section taken along the line c d ; letters as before. 
2 



26 ELEMENTARY PHYSIOLOGY. 

a longitudinal section shows us that the human body is a 
double tube, the two tubes being completely separated by the 
spinal column and the bony axis of the skull — the dorsal tube 
containing the cerebro-spinal axis ; the ventral, the alimentary 
canal, the sympathetic nervous system, and the heart, besides 
other organs. 

Transverse sections, taken perpendicularly to the axis of 
the vertebral column, or that of~ the skull, show still more 
clearly that this is the real fundamental structure of the human 
body, and that the great difference between the head and the 
trunk lies in the different size of the dorsal cavity relatively to 
the ventral. In the head the former cavity is very large in 
proportion to the size of the latter (Fig. 2) ; in the thorax or 
abdomen, it is very small (Fig. 3). 

The limbs contain no such chambers as the body and head ; 
but, with the exception of certain branching tubes filled with 
fluid, which are called vessels and lymphatics, are solid, or 
semi-solid, throughout. 

Such being the general character and arrangement of the 
parts of the human body, it will next be well to consider into 
what constituents it may be separated by the aid of no better 
means of discrimination than the eye and the anatomist's knife. 

Section III. — The Bodily Tissues. 

29. The Skin. — With no more elaborate aids than these, 
it becomes easy to separate that tough membrane which invests 
the whole body, and is called the skin, or integument, from the 
parts which lie beneath it. Furthermore, it is readily enough 
ascertained that this integument consists of two portions : a 
superficial layer, which is constantly being shed in the form of 
powder or scales, composed of minute particles of horny mat- 
ter, and is called the epidermis ; and of a deeper part, the c/^r- 
mis^ which is dense and fibrous. The epidermis, if wounded, 
neither gives rise to pain nor bleeds. The dermis, under like 
circumstances, is very tender, and bleeds freely. A practical 



THE BODILY TISSUES. 27 

distinction is drawn between the two in shaving, in the eourse 
of which operation the razor ought to cut only epidermic struc- 
tures ; for if it go a shade deeper, it gives rise to pain and 
hseraorrhage. 

30. Mucous Membranes. — The skin can be readily enough 
removed from all parts of the exterior, but at the margins of 
the apertures of the body it seems to stop, and to be replaced 
-by a layer which is much redder, more sensitive, bleeds more 
readily, and is rendered moist by giving out a more or less 
tenacious fluid, called mucus. Hence, at these apertures, the 
integument is said to stop, and to be replaced by mucous mem- 
hrane, which lines all those interior cavities, such as the ali- 
mentary canal, into which the apertures open. But, in truth, 
the integument does not come to an end at these points, but is 
directly continued into the mucous membrane, which last is 
simply an integument of greater delicacy, but consisting funda- 
mentally of the same two layers, a deep, fibrous, sanguine, and 
sensitive layer, and a superficial, horny, insensible, and blood- 
less one, now called the epithelium. Thus every part of the 
body might be said to be contained between the walls of a 
double bag, formed by the epidermis, which invests the outside 
of the body, and the epithelium, its continuation, which lines 
the internal cavities. 

31. Connective Tissue. — The dermis, and what answers to 
it in the mucous membranes, are chiefly made up by a fila- 
mentous substance, which yields abundant gelatine on being 
boiled, and is the matter which tans when hide is made into 
leather, and which is called areolar^ fibrous, or, better, connec- 
tive tissue.* The last name is the best, because this tissue is 
the great connecting medium by which the difterent parts of 
the body are held together. Thus it passes from the dermis be- 
tween all the other organs, en sheathing the muscles, coating the 
bones and cartilages, and eventually reaching and entering into 
the mucous membranes. And so completely and thoroughly 

♦Every such constituent of the body, as epidermis or epithelium, is called a 
"tissue;* 



28 ELEMENTARY PHYSIOLOGY. 

does the connective tissue permeate almost all parts of the 
body, that if every other tissue could be dissected away, a com- 
plete model of all the organs would be left composed of this 
tissue. Connective tissue varies very much in character; 
sometimes being very soft and tender, at others — as in the ten- 
dons and ligaments, which are almost wholly composed of it — 
attaining great strength and density. 

32. The Muscles.— Among the most important of the tis- 
sues imbedded in and ensheathed by the connective tissue, are 
some whose presence and action can be readily determined 
during life. 

If the upper arm of a man whose arm is stretched out, be 
tightly grasped by another person, the latter, as the man bends 
up his fore-arm, will feel a great mass which lies at the fore 
part of the arm, swell and become prominent. As the arm is 
extended again, the swelling vanishes. 

On removing the skin, the body which thus changes its 
configuration, is found to be a mass of red flesh, sheathed in 
connective tissue; and attached by the tendons, into which 
that tissue passes at each end, on the one hand, to the shoulder- 
bone, and on the other to one of the bones of the fore-arm. 
This mass of flesh is the muscle called biceps^ and it has the 
peculiar property of changing its dimensions — shortening and 
becoming thick in proportion to its decrease in length — by the 
influence of the will as well as by other stimuli. It is by reason 
of this property of muscular tissue that it becomes the great 
motor agent of the body ; the muscles being so disposed be- 
tween the systems of levers which support the body, that 
their shortening necessitates the motion of one lever upon 
another. 

33. The Cartilages and Bones. — These levers form part of 
the system of hard tissues which constitute the skeleton. The 
softer of these are the cartilages^ composed of a dense, firm sub- 
stance, ordinarily known as " gristle." The harder are the hones. 
which are masses either of cartilage or of connective tissue 
hardened by being impregnated with phosphate and carbonate 



THE BODILY TISSUES. 29 

of lime. They are animal tissues which have become, in a 
manner, naturally petrified; and when the salts of lime are ex- 
tracted, as they may be, by the action of acids, a model of the 
bone in soft and flexible animal matter remains. 

No fewer than 206 separate bones are ordinarily reckoned 
in the human body. Of these, thirty-eight enter into the com- 
position of the long axis, and five into that of the side walls of 
the cerebro-spinal cavity. Twenty-four ribs bound the chest 
laterally, twelve on each side, and most of them are connected 
by cartilages with the breast-bone. In the girdle which sup- 
ports the shoulder, two bones are reckoned ; in that to which 
the legs are attached, three. There are thirty bones in each 
of the arms, and in each of the legs. 

All these bones are fastened together by ligaments or by 
cartilages, and where they play freely over one another a coat 
of cartilage furnishes the surfaces which come into contact. 
The free surfaces of those articular cartilages which enter into 
a joint, again, are lined by a delicate synovial membrane, which 
secretes a lubricating fluid — the synovia. 

Section IV. — The Combination of Actions, 

34. How we stand upright. — Though the bones of the 
skeleton are all strongly enough connected together by liga- 
ments and cartilages, the joints play so freely, and the centre 
of gravity of the body, when erect, is so high up, that it is im- 
possible to make a skeleton, or a dead body, support itself in 
the upright position. That position, easy as it seems, is the 
result of the contraction of a multitude of muscles which op- 
pose and balance one another. Thus, the foot atfording the 
surface of support, the muscles of the calf (Fig. 4, 1.) must con- 
tract, or the legs and body would fall forw^ard. But this ac- 
tion tends to bend the leg ; and to neutralize this and keep the 
leg straight, the great muscles in front of the thigh (Fig. 4, 2) 
must come into play. But these, by the same action, tend to 
bend the body forward on the legs ; and if the body is to be 



30 



ELEMENTARY PHYSIOLOGY. 



kept straigbt, they must be neutralized by the action of the 
muscles of the buttocks and of the back (Fig. 4, IIL). 



Fig. 4. 

A Diagram hxttstrattng the Attachments op some of the most important 
Muscles which keep the Body in the erect Posture. 

L The muscles of the calf. II. Those of the back of the thigh. III. Those of the 
spine which tend to keep the body from falling forward. 

1. The muscles of the front of the leg. 2. Those of the front of the thigh. 3. 
Those of the front of the abdomen. 4, 5. Those of the front of the neck, which tend 
to keep the body from falling backward. 

The arrows indicate the direction of action of the muscles, the foot being fixed. 

The erect position, then, which we assume so easily and 
without thinking about it, is the result of the combined and 
accurately proportioned action of a vast number of muscles. 
What is it that makes them work together in this way ? 



THE COMBINATION OF ACTIONS. 31 

35. Relation of the Mind to the Muscles. — Let any per- 
son in the erect position receive a violent blow on the head, 
and you know what happens to hiin. On the instant he drops 
prostrate in a heap, with his hmbs relaxed and powerless. 
What has happened to him ? The blow may have been so in- 
flicted as not to touch a single muscle of the body ; it may not 
cause the loss of a drop of blood : and, indeed, if the " concus- 
sion," as it is called, has not been too severe, the sufferer, after 
a few moments of unconsciousness, will come to himself, and 
be as well as ever again. Clearly, therefore, no permanent in- 
jury has in this case been done to any part of the body, least 
of all to the muscles, but an influence has been exerted upon 
a something which governs the muscles. And this influence 
may be the effect of very subtle causes. A strong mental emo- 
tion, and even a very bad smell, will, in some people, produce 
the same effect as a blow. 

These observations might lead to the conclusion that it is 
the mind which directly governs the muscles, but a little fur- 
ther inquiry will show that such is not the case. For people 
have been so stabbed or shot in the back as to cut the spinal 
cord, without any considerable injury to other parts ; and in 
this case they lose the power of standing upright as much as 
before, though their minds may remain perfectly clear. And 
not only have they lost the power of standing upright under 
these circumstances, but they no longer retain any power of 
either feeling what is going on in the legs, or, by an act of 
their volition, causing motion in them. 

36. The Spinal Cord converts Impressions into Move- 
ments. — And yet, though the mind is thus cut oft' from the 
lower limbs, a controlling and governing power over them still 
remains in the body. For, if the soles of the disabled feet be 
tickled, though no sensation will reach the body, the legs will 
be jerked up just as would be the case in an uninjured person. 
And if a series of galvanic shocks be sent along the spinal cord, 
the legs will perform movements even more powerful than 
those which the will could produce in an uninjured person. 



32 eleme:ntary physiology. 

And, finally, if the injury is of such a nature that the cord is 
crushed or profoundly disorganized, all these phenomena cease ; 
tickling the soles, or sending galvanic shocks along the spine, 
will produce no eflfect upon the legs. 

By examinations of this kind carried still further, we amve 
at the remarkable result that the brain is the seat of all sensa- 
tion and mental action, and the primary source of all voluntary 
muscular contraction ; while the spinal cord is capable of re- 
ceiving an impression from the exterior, and converting it not 
only into a simple muscular contraction, but into a combina- 
tion of such actions. 

Thus, in general terms, we may say of the cei'ebro-spinal 
axis that it has the power of converting impressions from with- 
out into simple, or combined, muscular contractions. 

37. Special Sensations. — But you will further note that 
these impressions from without are of very different characters. 
Any part of the surface of the body may be so affected as to 
give rise to the sensations of contact, or of heat or cold ; and 
any and every substance is able, under certain circumstances, to 
produce these sensations. But only a very small part of the 
body is competent to be affected in such a manner as to pro- 
duce in us the sensations of taste or smell, of sight or of hear- 
ing; and only a few substances, or particular kind of vibrations, 
are able so to affect those localities. These limited parts of the 
body, which put us in relation with particular kinds of sub- 
stances, or forms of force, are what are termed sensory organs, 
of which we have two for sight, two for hearing, two for smell, 
and one, or more strictly two, for taste. 



Section V. — Nutrition, Circulation^ Excretion. 

38. Constant Renewal of Tissues. — And now that we 
have taken this brief view of the structure of the body, of the 
organs which support it, of the organs which move it, and of 
the organs which put it in relation with the surrounding world, 



NUTRITION, CIRCULATION, EXCRETION. 33 

or, in other words, enable it to move in harmony with in- 
fluences from without, we must consider the means by which 
all this wonderful apparatus is kept in working order. 

All work, as we have seen, implies waste. The work of the 
nervous system, and that of the muscles, therefore implies con- 
sumption either of their own substance or of something else. 
And as the organism can make nothing, it must possess the 
means of obtaining from without that which it wants, and of 
throwing from itself that which it wastes ; and we have seen 
that, in the gross, it does these things. The body feeds, and 
it excretes. But we must now pass from the broad fact to the 
mechanism by which the fact is brought about. The organs 
which convert food into nutriment are the organs of alimenta- 
tion ; those which distribute nutriment all over the body are 
organs of circulation ; those which get rid of the waste prod- 
ucts are organs of excretion. 

39. Alimentary Apparatus. — The organs of alimentation 
are the mouth, gullet, stomach, and intestines, with their ap- 
pendages. What they do is to receive and grind the food ; to 
act upon it with chemical agents, of which they have a store ; 
and in this way to separate it into a nutritious solution, and 
unnutritious dregs or fceces. 

40. Mechanism of Distribution. — A system of minute tubes, 
with very thin walls, termed capillaries, is distributed through 
the whole organism except the epidermis and its products, the 
epithelium, the cartilages, and the substance of the teeth, and, 
on all sides, these tubes open into others, which are called arte- 
ries and veins, and becoming larger and larger, at length open 
into the heart, an organ which, as we have seen, is placed m 
the thorax. During life, these tubes, and the chambers of the 
heart, with which they are connected, are all full of liquid, 
which is, for the most part, that red fluid with which we are all 
familiar as hlood. 

The Avails of the heart are muscular, and contract rhythmi- 
cally, or at regular intervals. By means of these contractions 
the blood which its cavities contain is driven in jets out oi 
2* 



34 ELEMENTARY PHYSIOLOGY. 

these cavities into the arteries, and thence into the capillaries, 
whence it returns by the veins into the heart again. 
This is the circulation of the blood, 

41. Exchanges of the Blood. — Now, the nutritive solu- 
tion which is formed by the process of digestion, traverses the 
thin membrane which separates the cavity of the alimentary 
canal from the innumerable cavities of the vessels in the walls 
of that canal, and so enters the blood, with which they are 
filled. Whirled thence by the torrent of the circulation, the 
blood, thus charged with nutritive matter, enters the heart, and 
is thence propelled into the organs of the body. To these or- 
gans it supplies the nutriment with which it is charged ; from 
them it takes their waste products, and so returns by the veins, 
loaded with useless and injurious excretions, which take the 
form, sooner or later, of water, carbonic acid, and urea. 

42. Drainage of Waste Matters from the Body. — These 
excretionary matters are separated from the blood by the excre- 
tory organSj of which there are three — the shin, the lungs, and 
the kidneys. 

Different as these organs may be in appearance, they are 
constructed upon one and the same principle. Each, in 
ultimate analysis, consists of a very thin membrane, with one 
face free, or in communication with the exterior of the body, 
and the other in contact with the blood which has to be purified. 
The excreted matters are, as it were, strained from the blood, 
through this membrane, on to its free surface, and thence make 
their escape. 

Every one of these organs eliminates ' the same products, 
viz., water, carbonic acid, and urea, or some nitrogenous com- 
pound of like import. But they eliminate them in various pro- 
portions, the skin giving olf much water, little carbonic acid, 
and still less urea ; the lungs giving off" much water, much car- 
bonic acid, and a minimum of urea, or ammonia (which is one 
of the products of the decomposition of urea) ; the kidneys sep- 
arating much water, much urea, and a minimum of carbonic acid. 

43. Double Function of the Lungs. — Finally, the lungs 



35 

play a double part, being not merely eliminators of waste, or 
excretionary products, but importers into the economy of a 
substance which is not exactly either food or drink, but some- 
thing as important as either, to wit, oxygen. It is oxygen 
which is the great sweeper of the economy ; which, introduced 
by the blood, into which it is absorbed, into all the corners of 
the organism, seizes upon those organic molecules which are 
broken down by their work, lays hold of their elements, and 
combines with them into the new and simpler foniis, carbonic 
acid, water, and urea. 

And in doing all this, the oxidation, or, in other words, the 
burning of these effete matters, gives rise to an amount of heat 
which is as eflScient as a fire to raise the blood to a temperature 
of about 100°; and this hot fluid, incessantly renewed in all 
parts of the economy by the torrent of the circulation, warms 
the body as a house is warmed by a hot-water apparatus. 



CHAPTER III. 

THE VASCULAE SYSTEM AND THE CIECULATION. 

Section I. — The Vascular System, 

44. Capillary Vessels. — Almost all parts of the body are 
vascular ; that is to say, they are traversed by minute and very 
close-set canals, which open into one another so as to consti- 
tute a small-meshed network, and confer upon these parts a 
spongy texture. The canals, or rather tubes, are provided with 
distinct but very delicate walls, composed of a structureless 
membrane, in which at intervals small oval bodies termed 
nuclei are imbedded. These tubes are the so-called capiUarics. 
They vary in diameter from -^Vo^^^ ^^ TlVo^^^ ^^ '^^^ i"<-'^^ ^ 
they are sometimes disposed in loops, sometimes in long, some- 
times in wide, sometimes in narrow meshes ; and the diameters 



36 



ELEMENTARY PHYSIOLOGY. 



of these meshes, or, in other words, the interspaces between the 
capillaries are sometimes hardly wider than the diameter of a 
capillary, sometimes many times as wide (Figs. 5, 6, 7, 8). 
These interspaces are occupied by the tissue which the capilla- 
ries permeate, so that the ultimate anatomical components of 
the body are, strictly speaking, outside the vessels, or extra- 
vascular. 

But there are certain parts which, in another and broader 
sense, are also said to be extra-vascular or non-vascular. These 
are the epidermis and epithelium, the nails and hairs, the sub- 
stance of the teeth, and the cartilages ; which may and do at- 
tain a very considerable thickness or length, and yet contain no 





Fig. 6. 










Fig. T. 



Fig. S. 



Fig. 5, Capillaries of muscle; Fig. 6, Looped capillaries of the finger; Fig. 7, Capil- 
laries of the lungs ; Fig. 8, Of fat. 



vessels. However, as we have seen that all the tissues are out- 
side the vessels, these differ only in degree from the rest. The 



THE VASCULAR SYSTEM. 61 

circumstance that all the tissues arc outside the vessels, by no 
means interferes with their being bathed by the fluid which is 
inside the vessels, for the walls of the capillaries are so exceed- 
ingly thin that their fluid contents readily exude through thena, 
and permeate the tissues in which they lie. 

45. The Smaller Arteries and Veins. — Of the capillary 
tubes thus described, one kind contains, during life, the red fluid, 
blood, while the others are filled with a pale, watery, or milky 
fluid, termed lymph or chyle. The blood-capillaries are contin- 
ued on diflerent sides into somewhat larger tubes with thicker 
walls, which are the smallest arteries and veins. 

The mere fact that the walls of these vessels are thicker 
than those of the capillaries, constitutes an important difference 
between the capillaries and the small arteries and veins ; for the 
walls of the latter are thus rendered far less permeable to fluids, 
and the irrigation of the tissues, which is effected by the capil- 
laries, cannot be performed by them. 




Fig. 9. 



A minute artery (a), endinir in (5) larsror and {c) smaller capillaries, d. Nuclei 
imbedded in the walls of the capillaries. 

The most important difference between these vessels and 
the capillaries, however, lies in the circumstance that their 
walls are not only thicker, but that they are more complex, 
being composed of several coats, one of which consists o( nuis- 



38 



ELEMENTARY PHYSIOLOGY. 



cular fibres (Fig. 11), which are directed transversely, so as to 
encircle the artery or vein (at a, Fig. 9). This coat lies in the 
middle ; inside it, and lining the cavity of the vessel, is a layer 
of very delicate epithelial cells (Fig. 10; Fig. 12, c). Outside 
the muscular layers is a sheath of fibrous tissue (a. Fig. 13). 
The muscular fibres themselves are flattened, spindle-shaped 
bands, each with an elongated rod-like nucleus in the middle 
(Fig. 11). 





Fia. 10. 



Fig. 11. 

Fig. 10.— Epithelial cells of the arteries. 

Fig. 11.— Muscular fibres of the arteries : the middle one treated with acetic acid 
shows more distinctly the nucleus a. 

46. Contractility of the Vascular Fibres. — When these 
fibres exercise that power of contraction, or shortening in the 
long and broadening in the narrow direction, which, as was 
stated in the preceding chapter, is the special property of mus- 
cular tissue, they, of course, narrow the calibre of the vessel, just 
as squeezing it in any other way would do, and this contraction 
may go so far as, in some cases, to reduce the cavity of the 
vessel almost to nothing, and to render it practically impervious. 

47. Circulating Vessels controlled by Nerves. — The state 
of contraction of these muscles of the small arteries and veins 
is regulated by the nerves supplied to the vessels, or, in other 



THE VASCULAR SYSTEM. 



59 



words, the nerves determine .whether the passage through these 
tubes shall be free and Avide, or narrow and obstructed. Thus, 
while the small arteries and veins lose the function of directly- 
irrigating the tissues, which the capillaries possess, they gain 
that of regulating the supply of fluid to the irrigators, or capil- 
laries themselves. The contraction or dilatation of the arteries, 
supplying a set of capillaries, comes to the same result as low- 
ering or raising the sluice-gates of a system of irrigation-canals. 





Fig. 12. Fig. 13. 

Fig. 12.— A small artery. 

Fig. 13.— A small vein, both treated with Mcetie acid; a fibrous coat; h muscular 
coat; c epithelial coat. 

48. Differences between Arteries and Veins. — The smaller 
arteries and veins severally unite into or are branches of larger 
arterial or venous trunks, which again spring from still larger 
ones, and these at length communicate by a few principal sepa- 
rate arterial and venous trunks with the heart. 

The smallest arteries and veins, as we have seen, are similar 
in structure, but the larger arteries and veins differ widely, for 
the larger arteries have walls so thick and stout that they do 
not sink together when empty ; and this thickness and stout- 
ness arises from the circumstance that, not only is the muscular 
coat very thick, but that in addition a strong coat of very 
elastic fibrous substance is developed outside the muscular 



40 ELEMENTAKY PHYSIOLOGY. 

layer. Thus, when a large artery is pulled out and let go, it 
stretches and returns to its primitive dimensions almost like a 
piece of india-rubber. 

The larger veins, on the other hand, contain but little either 
elastic or muscular tissue. Hence, their walls are thin, and 
they collapse when empty. 

This is one great difference between the larger arteries and 
the veins ; the other is the presence of what are termed valves 
in a great many of the veins, especially in those which lie in 
muscular parts of the body. 

49. Action of the Valves of the Veins. — These valves are 
pouch-like folds of the inner wall of the vein. The bottom of 
the pouch is turned toward those capillaries into which the 
vein opens. The free edge of the pouch is directed the other 
way, or toward the heart. The action of these pouches is to 
impede the passage of any fluid from the heart toward the cap- 
illaries, while they do not interfere with fluid passing in the 
opposite direction (Fig. 14). The working of some of these 
valves may be very easily demonstrated in the living body. 
When the arm is bared, blue veins may be seen running from 
the hand, under the skin, to the upper arm. The diameter of 



n 



Fig. 14. 

Diagrammatic Sections of Veins with Valves. 

In the upper, the blood is supposed to be flowing in the direction of the arrow, toward 
the heart ; in the lower, the reverse way. C capillary side ; H heart side. 

these veins is pretty even, and diminishes regularly toward the 
hand, so long as the current of the blood which is running in 
them from the hand to the upper arm is uninterrupted. 

But if a finger be pressed upon the upper part of one of 



THE VASCULAR SYSTEM. 



41 



these veins, and then passed downward along it, so as to drive 
the blood which it contains backward, sundry swellings, like 
little knots, will suddenly make their appearance at several 
points in the length of the vein, where nothing of the kind 
was visible before. These swellings are nothing more than the 
dilatations of the wall of the vein, caused by the pressure of 
the blood on that wall, above a valve which opposes its back- 
ward progress. The moment the backward impulse ceases the 
blood flows on again; the valve, swinging back toward the 
wall of the vein, affords no obstacle to its progress, and the dis- 
tension caused by its pressure disappears (Fig. 14). 

The only arteries which possess valves are the primary 
trunks — the aorta and pulmonary artery — which spring from 
the heart, and they will be best considered with the latter 
organ. 




Fig. 15. 

The Lymphatics op the Front op tife Rigiit Abm. 
f7 Lymphatic glands, or ganglia, as thoy arc sometimes called. Tliese ganglia 
arc not to be confounded with nervous ganglia. 



42 ELEMENTARY PHYSIOLOGY. 

50. The Lymphatics. — Besides the capillary network and 
the trunks connected with it, which constitute the blood -vascular 
system, all parts of the body which possess this system, except 
the brain and spinal cord, the eye-balls, the gristles, tendons, 
and perhaps the bones, also contain another set of what are 
termed lymphatic capillaries, mixed up with those of the blood- 
vascular system, but not directly communicating with them ; 
and, iiirther, differing from the foregoing in opening into larger 
vessels on only one side. That is to say, they are connected 
only with trunks which carry fluid away from them, there 
being none which bring any thing to them. These trunks re- 
semble the small veins not only in this respect, but, further, in 
being abundantly provided with valves, which fully allow of 
the passage of liquid from the lymphatic capillaries, but ob- 
struct the flow of any thing the other way. 

The lymphatic trunks differ from the veins, in that they do 
not rapidly unite into larger and larger trunks, which present a 
continually increasing calibre, and allow of a flow without in- 
terruption to the heart ; but that, remaining nearly of the same 
size, they, at intervals, enter and ramify in oval bodies called 
lymphatic glands, whence new lymphatic trunks arise (Fig. 15). 
In these glands the lymphatic capillaiies and passages are 
closely interlaced with blood capillaries. Sooner or later, 
however, the great majority of the smaller lymphatic trunks 
pour their contents into a considerable tube, which lies in front 
of the back-bone, and is called the thoracic duct ; this opens 
at the root of the neck into the conjoined trunks of the great 
veins which bring back the blood from the left side of the head 
and the left arm (Fig. 16). 

The remaining lymphatics are connected by a common 
canal with the corresponding vein on the right side. Where 
the principal trunks of the lymphatic system open into the 
veins, valves are placed, which allow of the passage of fluid 
only from the lymphatic to the vein. Thus the lymphatic ves- 
sels are, as it were, a part of the venous system, though, by 
reason of these valves, the fluid which is contained in the veins 



THE VASCULAR SYSTEM. 



43 



cannot get into the lymphatics. On the other hand, every 
facility is afforded for the passage of the fluid contained in the 
lymphatics into the veins. Indeed, in consequence of the nu- 
merous valves in the lymphatics, every pressure on, and con- 
ti'action of, their walls, not being able to send the fluid back- 
ward, must drive it more or less forward, toward the veins. 




Fig. 16. 
The TnoRAcic Duct. 
a The receptacle of the chyle: & the trunk of the thoracic duct, opening into the 
junction of the left juguhir (/) and subclavian (g) veins; </ lymphatic glands placed 
in the lumbar and intercostal regions ; 7ih the cut oesophagus. Two veins are soon 
running along beside the lower part of the thoracic duct, and just above its middle, 
one (the left) crosses under the duct and joins the other. These are the azygos 
veins. 

51. The Lacteals. — The lower part of the thoracic duct is 
dilated, and is termed the receptacle or cistern of the cJif/le (a, 
Fig. IG). In fiict, it receives the lymphatics of the intestines, 
which, though they differ in no essential respect from other 



44 ELEMENTARY PHYSIOLOGY. 

lymphatics, ar<> called lactealsy because, after a meal containing 
much fatty matter, they are filled with a milky fluid, which is 
termed the chijle. The lacteals, or lymphatics of the small in- 
testine not only form networks in its walls, but send blind pro- 
longations into the ,little velvety processes termed villi, with 
which the mucous membrane of that iutestine is beset. The 
trunks which open into the network lie in the mesentery (or 
membrane which suspends the small intestine to the back wall 
of the abdomen), and the glands through which these trunks 
lead are hence termed the mesenteric glands. 

Section IL — Connections and Structure of the Heart, 

52. The Heart and the Great Vessels. — It will now be 
desirable to take a general view of the arrangement of all these 
different vessels, and of their relations to the great central or- 
gan of the vascular system — the heart (Fig. 17). 

All the veins of every part of the body, except the lungs, 
the heart itself, and certain viscera of the abdomen, join to- 
gether into larger veins, which, sooner or later, open into one 
of two great trunks (Fig. 17, V.C.S, V,CJ,) termed the supe- 
rior and the inferior vena cava, which debouch into the upper 
or broad end of the right half of the heart. 

All the arteries of every part of the body, except the lungs, 
are more or less remote branches of one great trunk — the aoi^ta 
(Fig. 17, Ao,), which springs from the lower division of the left 
half of the heart. 

The arteries of the lungs are branches of a great trunk 
(Fig. 17, P,A,) springing from the lower division of the right 
side of the heart. The veins of the lungs, on the contrary, 
open by four trunks into the upper part of the left side of the 
heart (Fig. 17, P. F.). 

Thus the venous trunks open into the upper division of 
each half of the heart — those of the body in general into that 
of the right half; those of the lungs into the upper division of 
the left half; while the arterial trunks spring from the lower 



CONNECTIONS AND STRUCTURE OF THE HEART. 45 

moieties of each half of the heart — ^that for the body in gen- 
eral from the left side, and that for the lungs from the right 




Fig. 17. 

Diagram op the Heart and Vessels, ttitii the Course of the Circulation. 

L.A. left auricle ; X. V. left ventricle; Ao. aorta: A^. arteries to the upper part of tte 
body; -4^. arteries to the lower part of the body; 11. A. hepatic artery, wliioh eup- 
plies the liver with part of its blood ; Y'^. veins of the lower part of the body ; V.P. 
vena porta}; // F. hei>atic vein; V.C.I, inferior vena cava ; F.(^.<s\ superior vena 
cava; F^ veins of the upper part of the body; ^ff.^l. rijjht auricle; E.V. rijxht 
ventricle; P. A. jmlmonary artery ; Lg. lung; P. V. pulmonary vein ; Let. laeloals ; 
Ly. lymphatic; Th.D. thoracic duct. The arrows indicate the course of the bUn^d, 
lymph, and chyle. The vessels which contain arterial blood have dark contours, 
while those wliich carry venous blood have light contours. 



46 ELEMENTARY PHYSIOLOGY. 

side. Hence it follows that the great artery of the body, and 
the great veins of the body, are connected with opposite sides 
of the heart ; and the great artery of the lungs and its veins 
also wdth opposite sides ; while the veins of the body open 
into the same side as the artery of the lungs, and the veins of 
the lungs open into the same side as the artery of the body. 

53. Coronary Arteries and Vein. — The arteries which 
open into the capillaries of the substance of the heart are called 
coronary arteries^ and arise, like the other arteries, from the 
aorta, only close to its origin. But the coronary vein, which 
is formed by the union of the small veins which arise from the 
capillaries of the heart, does not open into either of the venae 
cava), but directly into the division of the heart into which 
these cavse open — tha't is to say, into the right upper division. 

54. Hepatic Vessels. — The abdominal viscera referred to 
above, the veins of which do not take the usual course, are the 
stomach, the intestines, the spleen, and the pancreas. These 
veins all combine into a single trunk, which is termed the vena 
portce (Fig. 17, F.P.), but this trunk does not open into the 
vena cava inferior. On the contrary, having reached the liver, 
it enters the substance of that organ, and breaks up into an 
immense multitude of capillaries, which ramify through the 
liver, and become connected with those into which the artery 
of the liver, called the hepatic artery (Fig. 17, H,A,\ tranches. 
From this common capillary mesh-work veins arise, and unite, 
at length, into a single trunk, the hepatic vein (Fig. 17, If.V,), 
which emerges from the liver, and passes into the inferior vena 
cava. The portal vein is the only great vein in the body which 
branches out and becomes continuous with the capillaries of an 
organ like an artery. 

55. The Heart. — The heart, to which all the vessels in the 
body have now been directly, or indirectly, traced, is an organ, 
the size of which is usually roughly estimated as equal to that 
of the closed fist of the person to whom it belongs, and which 
has a broad end turned upward and backward, and rather to 
the right side, called its base ; and a pointed end turned down- 



CONNECTIONS AND STRUCTURE OF THE HEART. 47 

ward and outward, and to the left side, so as to lie opposite 
the interval between the fifth and sixth ribs, which is called its 
apex (Fig. 19). 

It is lodged in the chest, between the lungs, nearer the 
front than the back wall of the chest, and it is enclosed in a 
sort of double bag — the pericardium — one- half of the double 
bag being closely adherent to the heart itself, while the other, 
which is continuous with this upon the great vessels, at a little 
distance from the base of the heart, loosely envelops the fore- 



A5^.a 




Transverse Section of the Chest, with the Heart and Lungsin Place. 

D. V. dorsal vertebra, or joint of the backbone; Ao. Ao'. aorta, the top of its arch 
beinj? cut away in this section; S.C. superior vena cava; P. A. pulmonary artery, 
dividing into a branch for each Inng; L.P. P.P. left and risrht pulmonary veins; 
i>V. bronchi; E.L. L.L. right and left lungs; (E. the gullet or oesophagus. 

going. Between the two layers of the pericardium is a small, 
completely closed cavity, lined by an epithelium, and secreting 
into its interior a small quantity of clear fluid. The outer 
layer of the pericardium is firmly connected with the upper 
surface of the diaphragm. 

But the heart cannot he said to depend altogether upon the 
diaphragm for support, inasmuch as the great vessels which 
issue from or enter it, and for the most part pass upward from 
its base, help to suspend it and keep it in place. 

56. The Auricles and Ventricles. — Thus the heart is 
coated outside by one layer of the pericardium. Inside, it con- 



48 



ELEMENTARY PHYSIOLOGY. 



tains two great cavities or " divisions," as tliey have been termed, 
above, completely separated by a fixed partition wbicli extends 
from the base to the apex of the heart, and consequently ha\dng 
no direct communication with one another. Each of these two 
great cavities is further subdivided, not longitudinally, but trans- 
versely, by a movable partition. The cavity above the parti- 



j?,er.x 



BI?Y 




Fig. 19. 

The HeapwT, great Vessels, and Lungs. Feont Yie w. 

B.V. right ventricle ; L.V. left ventricle; R.A. right auricle; L.A. left auricle; Ao. 
aorta; P. A. i)ulmonary artery ; P. V. pulmonary veins; P.L. right lung; L.L. left 
lung; F. 5. vena cava superior; /S.C. subclavian vessels; C. carotids; P. and 
L.J.V. right and left jugular veins: V.l. vena cava inferior; T. trachea; B. 
bronchi. 

tion on each side is called the auricle — right or left, as the case 
may be ; the cavity below the partition is called the ventricle 
of its side. 

Each of the four cavities has the same capacity, and is ca- 
pable of containing from four to six cubic inches of water ; but 
the walls of the auricles are much thinner than those of the ventri- 
cles, and are of equal thickness, while, of the ventricles, the left 
has a much thicker wall than the right. 

57. Their unequal Work. — In fact, as we shall see, the 
ventricles have more work to do than the auricles, and the left 
ventricle more to do than the right. Hence the ventricles have 



CONNECTIONS AND STRUCTURE OF THE nEAP.T. 



49 



more muscular substance than the auricles, and the left ventri- 
cle than the right; and it is this excess of muscular substance 
which gives rise to the excess of thickness observed. 



Y.CX 




31^: 



Fig. 20. Fig. 21. 

Fig. 20, the Left Side, and Fig. 21, the Eight Side of the Heart dissected. 

Fig. 20. — Z..4. the left auricle; P.V. the four pulmonary veins ; c d, a. style passed 
through the auriculo-ventricular aperture ; M. V. the mitral valves ; a &, a style 
passed through the left ventricle into the aorta; B,A. R. V, parts of the right side 
of the heart; /".J. pulmonary artery. 

Fig. 21 . — R.A. the right auricle ; V. ( \>S. superior vena cava ; V.C.IA nfei-ior vena ca va, 
the styles/^, c d being passed through them into the auricls; a ?>, style passed 
through the auriculo-ventricular aperture ; T. V. tricuspid valve; li. V. right ven- 
tricle; 8.L. semilunar valves at the base of P. A. the pulmonary artery, through 
which the style g h\& passed ; L.A. L. V. parts of the left side of the heart. 



58. Muscular Fibres and Fibrous Rings. — The muscular 
fibres of the heart are not smooth, nucleated bands, like those 
of the vessels, but are bundles of transversely-striped fibres, and 
resemble those of the chief muscles of the body, except that 
they have no sheath or sarcolemma, such as we shall find to 
exist in the latter. 

Almost the whole mass of the heart is made up of these 
muscular fibres, which have a very remarkable and complex 
arrangement ; but it has an internal lining called the endocar- 
dium ; and at the junction between the auricles and ventricles 
the apertures of communication between their cavities, called 
3 



50 ELEMENTARY PHYSIOLOGY. 

the auriculo-ventricular apertures, are streDgthened by fibrous 
rings. To these rings the movable partitions or valves be- 
tween auricles and ventricles, the arrangement of which must 
next be considered, are attached. 

59. Valves of the Heart ; their Structure and Action. — 
There are three of these partitions to the right auriculo-ventric- 
ular aperture, and two to the left. Each is a broad, thin, but 
very tough and strong production of the endocardium, of a tri- 
angular shape, attached by its base, which joins on to its fellow, 
to the auriculo-ventricular ring, and at its apex depending into 
the ventricular cavity. On the right side there arc, therefore, 
three of these broad, pointed membranes, whence the whole 
apparatus is called the tricuspid valve. On the left side there 
are but two, which when detached from all their connections 
but the auriculo-ventricular ring, look something like a bishop's 
mitre, and hence this is called the mitral valve. 

The edges aod apices of the valves are not completely free 
and loose. On the contrary, a number of fine but strong ten- 
dinous cords, called chordce tendinece, connect them with some 
column -like elevations of the fleshy substance of the walls of 
the ventricle, which are termed columnce carnece. 

From this arrangement it follows that the valves oppose no 
obstacle to the passage of fluid from the auricles to the ventri- 
cles ; but if any should be forced the other way, it will at once 
get between the valve and the wall of the heart and drive the 
valve backward and upward. Partly because they -soon meet 
in the middle and oppose one another's action, and partly be- 
cause the chordce tendimce hold their edges and prevent them 
from going back too far, the valves thus forced back give 
rise to the formation of a complete transverse partition, 
through which no fluid can pass between the ventricle and the 
auricle. 

Where the aorta opens into the left ventricle and where the 
pulmonary artery opens into the right ventricle, another valvu- 
lar apparatus is placed, consisting in each case of three pouch- 
like valves similar to those of the veins, and called the semilu- 



CONNECTIONS AND STEUCTUEE OF THE HEART. 



51 



nar valves^ but placed on the same level and meeting on the 
middle line, so as completely to stop the passage when any 
fluid is forced along the artery toward the heart. On the other 
hand, these valves flap back and allow any fluid to pass from 
the heart into the artery with the utmost readiness. 

The action of the auriculo-ventricular valves may be demon, 
strated with great ease on a sheep's heart, in which the aorta 
and pulmonary artery are tied and the greater part of the auri- 
cles cut away, by pouring water into the ventricles through the 
auriculo-ventricular aperture. The valves then usually close 
themselves, and they may be made to do so at once by gently 
squeezing the ventricles. So, in like manner, if the base of the 
aorta or pulmonary artery be cut out of the heart so as not to 
injure the valves, water poured into the upper ends of these 
vessels will cause the valves to close tightly, and allow nothing 
to flow out after the first moment. 




FiQ. 22. 



The valves of the heart displayed by cuttins: away both auricles and all but the bases 
and aorta {B^\ C, the tricuspid; D, the mitral 



of the i)ulmonary artery (A) and .,y,,^.„ yu^ , , 
valve ; a, a style passed into the coronary vein. 



Thus the arrangement of the auriculo-ventricular valves is 
such that any fluid contained in the chambers of the heart can 
be made to pass through the auriculo-ventricular apertures in 



52 ELEMENTARY PHYSIOLOGY. 

only one direction, that is to say, from the auricles to the ven- 
tricles; and on the other hand, the arrangement of the semilu- 
nar valves is such that fluid in the ventricle passes easily into 
the aorta and pulmonary artery, but that none can be made to 
travel the other way from the artery to the ventricle. 

60. Rhythm of its Movement— Systole and Diastole. — 
Like all other muscular substances, that of the heart is contrac- 
tile ; but unlike most muscles, the heart contains within itself 
a something which causes its different parts to contract in a 
definite succession and at regular intervals. If the heart of a 
living animal be removed from the body, it will go on pulsating 
for a longer or shorter time, much as it did while in the body. 
And carefal attention to these pulsations will show that they 
consist of — (1) A simultaneous contraction of the walls of both 
auricles. (2) Immediately following this, a simultaneous con- 
traction of the walls of both ventricles. (3) Then comes a 
pause or state of rest, after which the auricles and ventricles 
contract again in the same order as before, and their contrac- 
tions are followed by the sam.e pause as before. 

If the auricular contraction be represented by A'', the ven- 
tricular by V, and the pauses by — , the series of actions will 
be as follows : A" V^ — ; A^ V^ _ ; A^ V^ — ; etc. Thus, 
the contraction of the heart is rhythmical, two short contrac- 
tions of its upper and lower halves respectively being followed 
by a pause of the whole, which occupies about as long as the 
two contractions. 

The state of contraction of the ventricle or auricle is called 
its systole — the state of relaxation, during which it undergoes 
dilatation, its diastole. 

Section III. — Working of the Heart and Vessels, 

61. Working of the Heart. — Having now acquired a 
' notion of the arrangement of the different pip'es and reservoirs 

of the circulatory system, of the distribution of the valves, and 
of the rhythmical contractions of the heart, it will be easy to 



WORKING OF THE HEART AND VESSELS. 53 

comprehend what must happen if (the whole apparatus con- 
taining blood) the first step in the pulsation of the heart occurs 
and the auricles contract. By this action each auricle tends 
to squeeze the fluid which it contains out of itself in tv/o direc- 
tions — the one toward the great veins, the other toward the 
ventricles ; and the direction which the blood as a whole will 
take will depend upon the relative resistance offered to it in 
these two directions. Toward the great veins it is resisted by 
the whole mass of the blood contained in the veins. Toward 
the ventricles, on the contrary, there is no resistance worth 
mentioning, inasmuch as the valves are open. The walls of the 
ventricles, in their uncontracted state, are flaccid and easily dis- 
tended, and the whole pressure of the arterial blood is taken off 
by the semilunar valves, which arc necessarily closed. There- 
fore, when the auricle contracts only a very little of the fluid will 
flow back into the veins, and the great mass of it will pass at 
once mto the ventricles. As the ventricles become distended, 
the blood getting behmd the auriculo-ventricular valves will 
bring them toward one another, and almost shut them. The 
auricles now cease to contract, and immediately that their walls 
relax, fresh blood from the great veins flows into and slowly 
distends them again. 

But the moment the auricular systole is over, the ventricu- 
lar systole begins. The walls of each ventricle contract vigor- 
ously, and the first effect of that contraction is to shut the au- 
riculo-ventricular valves completely, and to stop all egress tov/- 
ard the auricle. The pressure upon the valves becomes very 
considerable, and they might even be driven upward if it were 
not for the chordce tendinece which hold down their edo'es. 

Furthermore, as the contraction continues, and the cavity 
of the ventricle becomes diminished, the points of the wall of 
the heart to which the chordce tendinece are attached approach 
the edges of the valves, and thus there is a tendency to allow 
of a slackening of these cords, which, if it really took place, 
might permit the edges of the valves to flap back and so de- 
stroy their utility. This tendency, however, is counteracted by 



54 ELEMENTARY PHYSIOLOGY. 

the coDiiGction of the chorda; tendinece not directly to the walls 
of the heart, but to those muscular pillars, the columnce cornece, 
which stand out from its substance. These muscular pillars 
contract at the same time the substance of the heart does ; and 
thus, just so far as the contraction of the latter brings them 
nearer the valves, do they, by their own contraction, pull the 
chordae, te7idinece as tight as before. 

By the means which have now been described the fluid in 
the ventricle is debarred from passing back into the auricle ; 
the whole force of the contraction of the ventricular walls is 
therefore expended in overcoming the resistance presented by 
the pressure of the blood in the arteries on the semilunar 
valves, which is the result partly of the weight of that fluid, 
partly of the clastic resistance of the arterial walls to further 
distension, and partly of the friction and inertia of the blood 
contained in the arterial ramifications and capillaries. It now 
becomes obvious why the ventricles have so much more to da 
than the auricles, and why valves are needed between the auri- 
cles and ventricles, while none are w^anted betw^een the auricles 
and the veins. 

All that the auricles have to do is to fill the ventricles, 
which offer no active resistance to that process. Hence the 
thinness of the w^alls of the auricles, and hence the needlessness 
of any auriculo- venous valve, the resistance on the side of the 
ventricle being so insignificant that it gives w^ay at once before 
that afforded by the pressure of the blood m the veins. On the 
other hand, the ventricles have to overcome a great resistance 
in order to force fluid into elastic tubes which are already full ; 
and if there w^ere no auriculo-ventricular valves, the fluid in the 
ventricles would meet with less obstacle in pushing its w^ay 
backward into the auricles and thence into the veins than in 
lifting the semilunar valves. Hence the necessity, firstly, of the 
auriculo-ventricular valves; and secondly, of the thickness and 
strength of the walls of the ventricles, and since the aorta, body, 
capillaries, and veins form a much larger system of tubes, con- 
taining more fluid and offering more resistance than the pulmo- 



WORKING OF THE HEART AND VESSELS. 55 

nary arteries, capillaries, and veins, it follows that the left ven- 
tricle needs a thicker muscular wall than the right. 

62. The Working of the Arteries, — Thus, at every systole 
of the auricles, the ventricles are filled and the auricles emptied, 
to be slowly refilled by the pressure of the fluid in the great 
veins, which is amply sufficient to overcome the passive resist- 
ance of their relaxed walls. And at every systole of the ven- 
tricles the arterial systems of the body and lungs receive the 
contents of these ventricles, and the nearly emptied ventricles 
remain ready to be refilled by the auricles. 

We must now consider what happens in the arteries. 
When the contents of the ventricles are suddenly forced into 
these tubes (which are already full), a shock is given to the 
whole mass of fluid which they contain. This shock is propa- 
gated almost instantaneously throughout the fluid, becoming 
fainter and fainter in proportion to the increase of its mass in 
the capillaries, and finally cease to be discernible. If the vessels 
were tubes of a rigid material, like gas-pipes, the fluid which 
the arteries contain would be transported forward as far as this 
impulse was competent to caiTy it, at the same instant as the 
shock throughout their whole extent ; and as the arteries open 
into the capillaries, the capillaries into the veins, and these into 
the heait, there would be returned to the auricles almost at the 
same moment that the ventricles contract a quantity of fluid 
exactly equal to that driven out of the ventricles. 

However, the vessels are not rigid, but, on the contrary, 
very yielding tubes; and the great arteries, as we have seen, 
have especially elastic walls. What happens then when the 
ventricular systole takes place is — 1st, The sudden slight shock 
already mentioned. 2d, The dilatation of the great arteries by 
the pressure of the Increased quantity of blood forced into 
them. 

Finally, when the systole is over, the force stored up in the 
dilated arterial walls in the shape of elastic tension, ooniesinto 
play and exerts a pressure on the fluid — the first eftect of which 
is to shut the semilunar valves; the second, to drive the fluid 



56 ELEMENTAEY PHYSIOLOGY. 

from the larger arteries along the smaller ones. These it di- 
lates in the same fashion. The fluid then passing into the cap- 
illaries, the ejection of a corresponding quantity of fluid from 
them into the veins, and finally from the veins into the heart, 
is the ultimate result of the ventricular systole. 

63. The Beat of the Heart. — Several of the practical re- 
sults of the working of the heart and arteries just described 
now become intelligible. For example, between th6 fifth and 
sixth ribs, on the left side, a certain movement is perceptible by 
the finger and by the eye, which is known as the heating of the 
heart. It is the result of the striking of the apex of the heart 
against the pericardium and through it, on the inner wall of 
the chest, at this point at the moment of the systole of the 
ventricles. When the systole occurs, in fact, two things happen : 
in the first place, in consequence of the manner in which the 
muscular fibres of the heart are disposed, its apex bends upward 
sharply, and in the second place, its face is thrown a little 
downward and forward in consequence of the stretching and 
elongation of the aorta by the blood which is thrown into it. 

The result of one or other, or both of these actions com- 
bined, is the upward and forward blow of the apex of the heart 
which we feel. 

64. The Sounds of the Heart.— Secondly, if the ear is ap- 
plied over the heart certain sounds are to be heard, which re- 
cur with great regularity at intervals corresponding with those 
of every two beats. First comes a longish dull sound ; then a 
short sharp sound ; then a pause ; then the long, then the sharp 
sound, then another pause, and so on. There are many differ- 
ent opinions as to the cause of the first sound, and perhaps 
physiologists are not yet at the bottom of the matter; but the 
second sound is without doubt caused by the sudden closure 
of the semilunar valves when the ventricular systole ends. 
That such is the case is proved by the experiment which has 
been performed of hooking back the semilunar valves in ali\dng 
animal, when the second sound ceases at once. 

65. The Pulse in the Arteries. — Thirdly, if the finger be 



WOKKING OF THE HEART AND VESSELS. 57 

placed upon an artery, such as that at the wrist, what is termed 
the pulse will be felt ; that is to say, the elastic artery dilates 
somewhat at regular intervals, which answer to the beatings of 
the heart. The pulse which is felt by the finger, however, does 
not correspond precisely with the beat of the heart, but takes 
place a little after it, and the interval is longer the further the 
artery is from the heart. The beat in the artery on the inner 
side of the ankle, for example, is a little later than the beat of 
the artery in the temple. The reason of this is that the finger 
is only delicate enough to distinguish the dilatation of the ar- 
tery by the wave of blood which is driven along it by the 
elastic reaction of the aorta, and is not competent to perceive 
the first shock caused by the systole. But if instead of the 
fingers very delicate levers be made to rest upon any two arte- 
ries, it will be found that the pulse really begins at the same 
time in both, the shock of the systole making itself felt all over 
the muscular system at once ; and that it is only the actual fluid 
which is propelled into the two arteries by the elastic reaction 
of the greater vessels, which takes longer to reach and distend 
the more distant branch. 

66. Jetting of Blood from cut Arteries. — Fourthly, 
when an artery is cut the outflow of the fluid which it contains 
is increased by jerhs^ the intervals of which correspond with the 
intervals of the beats of the heart. The cause of this is plainly 
the same as that of the pulse; the force which w^ould be em- 
ployed in distending the walls of the artery, were the latter en- 
tire, is spent in jerking the fluid out when the artery is cut. 

67. Why the Capillaries are Pulseless.— Fifthly, The 
pulse, under ordinary circumstances, is no longer to be de- 
tected in the capillaries nor in the veins. This arises from 
several circumstances. One of them is that the capacity 
of the branches of an artery is greater than the capacity of 
the trunk, and the capacity of the capillaries is greater than 
that of the small arteries. Hence, supposing the capacity of 
the trunk to be 10, that of its branches 50, and that of the cap- 
illaries into which these open 100, it is clear that a quantity 

3* 



58 ELEMENTAEY PHYSIOLOGY. 

of fluid thrown into the trunk, sufficient to dilate it by one- 
tenth, and to produce a very considerable and obvious effect, 
could not distend each branch by more than -/-Qth, and each 
capillary by y-J-gth of its volume in amount, an effect which 
might be quite imperceptible. 

68. Subdivision of the Heart-Stroke.— Furthermore, the 
flow of the fluid is retarded by the subdivision of the tubes 
which contain it ; and the multitude of minute impulses into 
which the primary blow of the systole is subdivided in the 
small vessels, become lost among these obstacles and fused into 
one general and steady pressure. This loss of the distinct effect 
of the heart's action may be likened to the result of pumping into 
a horse-trough. Where the water flows into the trough, the 
splashes and waves, caused by the intermitting fall of water 
from the pump, are very obvious ; but from a tap open at the 
other end of the trough, the water will flow steadily and 
evenly. 

69. Cause of a steady Capillary Flow. — Finally, in con- 
sequence of the resistance to the passage of the fluid, resulting 
from the extremely minute size and subdivision of the capilla- 
ries, the fluid to a certain extent accumulates in the arteries, 
and keeps their walls in a constant state of distension, which is 
only increased at each successive beat of the heart. In other 
words, on^ beat follows another before the effect of the first has 
ceased. As the effect of each systole becomes diminished by 
the causes above mentioned, that of this constant pressure be- 
comes more obvious and gives rise to a steady passage of the 
fluid from the arteries toward the veins. In this way in fact 
the arteries perform the same functions as the air-reservoir of 
a fire-engine, which converts the jerking impulse given by the 
pumps into the steady flow of the delivery-hose. 

Such is the general result of the mechanical conditions of 
the organs of the circulation combined with the rhythmical 
activity of the heart. This activity drives the fluid contained 
in these organs out of the heart into the arteries, thence to the 
capillaries, and from them through the veins to the heart 



THE GENERAX, CIRCULATION. 59 

ap*aiii ; and in the course of these operations it gives rise inci- 
dentally to the beating of the heart, the sounds of the heart, 
and the pulse. 

Section IV. — The General Circulation, 

70. The Course of the Circulation. — It is now neces- 
sary to trace the exact course of the circulation as a whole. 
And we may conveniently commence with the portion of 
the blood contained at any moment in the right auricle. 
The contraction of the right auricle drives that fluid, for the 
reason above mentioned, into the right ventricle ; the ventricle 
then contracts and forces it into the pulmonary artery ; from 
hence it passes into the capillaries of the lungs. Leaving 
these, it returns by the four pulmonary veins to the left auri- 
cle ; the contraction of the left auricle drives it into the left 
ventricle ; that of the left ventricle forces it into the aorta. 
The branches of the aorta convey it into all parts of the body 
except the lungs, and from the capillaries of all these parts, ex- 
cept the intestines and certain other viscera in the abdomen, 
it is conveyed by vessels which gradually unite into larger and 
larger trunks into either the superior or the inferior vena cava, 
which carry it to the right auricle once more. But the blood 
brought to the capillaries of the stomach and intestines, spleen 
and pancreas, by these arteries is gathered into veins which unite 
into a single trunk — the vena portos. The vena poilae distributes 
its blood to the liver, mingling with that supplied to the capilla- 
ries of the same organ by the hepatic artery. From these capil- 
laries it is conveyed by small veins which unite into a large 
trunk — the hepatic vein^ which opens into the inferior vena cava. 
This course of the blood from the abdominal viscera to the 
hepatic vein is called the portal circulation. 

The heart itself is supplied wdth blood by the two coronary 
arteries which spring from the root of the aorta just above two 
of the semilunar valves. The blood from the capillaries of the 
heart is carried back by the coronary vein, not to cither vena 



60 ELEMENTARY THYSIOLOGY. 

cava, but to the right auricle, its openiDg into which is pro- 
tected by a valve, so as to prevent the right auricle from driv* 
ing the venous blood which it contains back into the vessels 
of the heart. 

71. Routes of the Travelling Blood-Particles. — Thus, the 
shortest possible course which any particle of the blood can 
take, in order to pass from one side of the heart to the other, 
IS to leave the aorta by one of the coronary arteries, and return 
to the right auricle by the coronary vein. And in order to 
pass through the greatest possible number of capillaries, and 
return to the point from which it started, a particle of blood 
must leave the heart by the aorta and traverse the arteries 
which supply the alimentary canal, spleen, and pancreas. It 
then enters, Istly, the capillaries of these organs; 2dly, the 
capillaries of the liver; 3dly, after passing through the right 
side of the heart, the capillaries of the lungs, from which it re- 
turns to the left side and eventually to the aoila. 

Furthermore, from what has been said respecting the lym- 
phatic system, it follows that any particle of matter which enters 
a lacteal of the intestine will reach the right auricle by the 
superior cava, after passing through the lymph capillaries and 
channels of sundry lymphatic glands; while any thing which 
enters the adjacent blood capillary will reach the right auricle 
by the inferior cava, after passing through the blood capillaries 
of the liver. 

72. Nervous Control and the Circulation — We have seen 
that the small arteries and veins may be directly affected by 
the nervous system, which controls the state of contraction of 
their muscular walls, and so regulates their calibre. The effect 
of this powder of the nervous system is to give it a certain con- 
trol over the circulation in particular spots, and to produce 
such a state of affairs, that, although the power of the heart and 
the general condition of the vessels remain the same, the state 
of the circulation may be very different in different localities. 

73. Explanation of Blushing. — Blushing is such a purely 
local modification of the circulation, so that it will be instructive 



THE GENERAL CIRCULATION. 61 

to consider what happens in blushing. An emotion — some- 
times pleasurable, sometimes painful — takes possession of the 
mind, thereupon a hot flush is felt, the skin grows red, and ac- 
cording to the intensity of the emotion these changes are con- 
fined to the cheeks only, or extend to the " roots of the hair," 
or " all over." 

What is the cause of these changes? The blood is a red 
and hot fluid ; the skin reddens and grows hot because its ves- 
sels suddenly contain an increased quantity of this red and hot 
fluid ; and its vessels contain more, because the small arteries 
suddenly dilate, the natural moderate contraction of their mus- 
cles being superseded by a state of relaxation. In other words, 
the action of the nerves which cause this muscular contraction 
is suspended. On the other hand, in many people, extreme 
terror causes the skin to grow cold and the face to appear pale 
and pinched. Under these circumstances, in fact, the supply of 
blood to the skin is greatly diminished, in consequence of an 
excessive stimulation of the nerves of the small arteries, which 
causes them to contract and so cut off the supply of blood. 

74. Experimental Proof of this. — That this is the real state 
of the case may be proved experimentally upon rabbits. 
These animals, it is true, do not blush naturally, but they may 
be made to blush artificially. If, in a rabbit, the sympathetic 
nerve which sends branches to the vessels of the head is cut, 
the ear of the rabbit, which is covered by so delicate an integ- 
ument that the changes in its vessels can be readily perceived, 
at once blushes. That is to say, the vessels dilate, fill with 
blood, and the ear becomes red and hot. The reason of this 
is, that when the sympathetic is cut, the nervous stinnilus 
which is ordinarily sent along its branches is interrupted, and 
the muscles of the small vessels, which were slightly contracted, 
become altogether relaxed. 

And now it is quite possible to produce pallor and cold in 
the rabbit's ear. To do this it is only necessary to irritate the 
cut end of the sympathetic which remains connected with the 
vessels. The nerve then becomes excited, so that the muscu- 



62 ELEMEKTAEY PHYSIOLOGY. 

lar fibres of the vessels are thrown into a violent state of con- 
traction, which diminishes their calibre so much that the blood 
can hardly make its way through them. Consequently, the 
ear becomes pale and cold. 

75. Relation of this Nervous Control to Disease. — The 
practical importance of this local control exerted by the ner- 
vous system is immense. When exposure to cold gives a man 
catarrh, or inflammation of the lungs, or diarrhoea, or some 
still more serious affection of the abdominal viscera, it is 
brought about in this way. The impression made by the cold 
on the skin is conveyed to the nervous centres, and so influen- 
ces the vaso-motor nerves, as the nerves which govern the walls 
of the vessels are called (see Chapter I.), of the organ affected, 
as to cause their partial paralysis, and produce that state of 
congestion (or undue distension of the vessels) which so com- 
monly ends in inflammation. 

76. Nervous Control over the Heart. — Is the heart, in 
like manner, under the control of the central nervous system? 

As we all know, it is not under the direct influence of the 
will, but every one is no less familiar with the fact that the 
actions of the heart are wonderfully affected by all fornas of 
emotion. Men and women often faint, and have sometimes 
been killed, by sudden and violent joy or sorrow ; and when 
they faint or die in this way, they do so because the perturba- 
tion of the brain gives rise to a something which arrests the 
heart as dead as you stop a stop-watch with a spring. On the 
other hand, other emotions cause that extreme rapidity and 
violence of action which we call palpitation. 

Now there are three sets of nerves in the heart: one set 
are supplied by ganglia, or masses of nerve-cells, in its sub- 
stance ; another set come from the sympathetic nerve ; a third 
set are branches of a remarkable nerve, which comes straight 
from the brain, and is called the pneumogastric nerve. There 
is every reason to believe that the regular rhythmical succes- 
sion of the ordinary contractions of the heart depends upon 
the ganglia lodged in its substance. At any rate, it is certain 



THE GENEEAI. CmCULATION. 63 

that these movements depend neither on the sympathetic nor 
on the pneumogastric, since they go on as well when the heart 
is removed from the body. 

In the next place, there is much reason to believe that the 
influence which increases the rapidity of the heart's action is 
exerted through the sympathetic. 

And, lastly, it is quite certain that the influence which 
arrests the heart's action is supplied by the pneumogastric. 
This may be demonstrated in animals, such as frogs, with great 
ease. 

77. The Circulation directly observed .—If a frog be pithed, 
or its brain destroyed, so as to obliterate all sensibility, the 
animal will continue to live, and its circulation will go on per- 
fectly well for an indefinite period. The body may be laid 
open without causing pain or other disturbance, and then the 
heart will be observed beating with great regularity. It is pos- 
sible to make the heart move a long index backward and for- 
ward, like the inverted pendulum which musicians term a met- 
ronome ; and if frog and index are covered with a glass shade, 
the air under which is kept moist, the index will vibrate with 
great steadiness for a couple of days. 

It is easy to adjust to the frog thus prepared, a contrivance 
by which electrical shocks may be sent through the pneumo- 
gastric nerves, so as to irritate them. The moment this is 
done the index stops dead, and the heart will be found quies- 
cent, with relaxed and distended walls. After a little time the 
influence of the pneumogastric passes off, the heart recommen- 
ces its work as vigorously as before, and the index vibrates 
through the same arc as formerly. With careful management, 
this experiment may be repeated very many times ; and after 
every arrest by the irritation of the pneumogastric, the heart 
resumes its work. 

78. Proof of the Circulation in Man. — The evidence that 
the blood circulates in man, although perfectly conclusive, is 
almost all indirect. But certain of the lower animals, the 
whole, or parts, of the body of ^vhich are transparent, readily 



64 



ELEMENTARY PHYSIOLOGY. 



afford direct proof of the circulation, the blood visibly rushing 
from the arteries into the capillaries, and from the capillaries 




Fig. 24. 

Fig. 23.— Two toes of a frog's foot, with the intervening web, slightly enlarged; o, 
veins ; 6, arteries connected by a network of capillaries. 

Fig. 24. — A small portion of the net-work magnitied ; a b are small veins, and d capil- 
laries, all full of large oval blood corpuscles, moving in the direction indicated 
by the arrows ; c, star-shaped, colored patches or pigment cells in the frog's 
skin. 



into the veins, so long as the animal is alive and its heart is at 
work. The animal in which the circulation can be most con- 
veniently observed is the frog, as the web between its toes is 
very transparent, and the particles suspended in its blood are 
so large that they can be readily seen as they slip swiftly along 



ITS MICKOSCOPICAL ELEMENTS. 65 

with the stream of blood, when the toes are fastened out, and 
the intervening web examined under even a low magnifying 
power (Fig. 24). 



CHAPTER IV. 

OF THE BLOOD AND LYMPH. 

• Section I. — Its Microscopical Elements, 

79. How to examine it. — In order to become properly ac- 
quainted With the characters of the blood it is necessary to ex- 
amine it with a microscope, magnifying at least three or four 
hundred diameters. Provided with this instrument, a hand 
lens, and some slips of thick and thin glass, the student will be 
enabled to follow the present chapter. 

The most convenient mode of obtaining small quantities 
of blood for examination, is to twist a piece of string, pretty 
tightly, round the middle of the last joint of the middle or 
ring finger of the left hand. The end of the finger will im- 
mediately swell a little, and become darker colored, in con* 
sequence of the obstruction to the return of the blood in the 
veins, caused by the ligature. When in this condition, if it be 
lightly pricked with a sharp clean needle (an operation which 
causes hardly any pain), a good-sized drop of blood will at 
once exude. Let it be deposited on a glass slide, and covered 
lightly and gently with a thin glass, so as to spread it out 
evenly into a thin layer. Let a second slide receive another 
drop, and let it be put under an inverted tumbler so as to keep 
it from drying. Let a third drop be dealt with in the same 
way a few granules of common salt being first added to the 
drop. 

80. Its Appearance whenmagnified. — To the naked eye 
the layer of blood upon the first slide will appear of a pale rod- 
dish color, and quite clear and homogeneous. But on viewing 



66 ELEMENTARY PHYSIOLOGY. 

it with even a pocket lens, its apparent homogeneity will dis- 
appear, and it will look like a mixture of excessively fine yel- 
lowish-red particles, like sand, or dust, with a watery, almost 
colorless, fluid. Immediately after the blood is drawn the par- 
ticles will appear to be scattered very evenly through the fluid, 
but by degrees they aggregate into minute patches, and the 
layer of blood becomes more or less spotty. 

The "particles" are what are termed the corpuscles of the 
blood ; the nearly colorless fluid in which they arc suspended 
is \\\Q plasma, 

81. Coagulation. — The second slide may noAv be exam- 
ined. The drop of blood will be unaltered in form, and may 
perhaps seem to have undergone no change. But if the slide 
be inclined it will be found that the drop no longer flows ; 
and, indeed, the slide may be inverted without the disturbance 
of the drop, which has become solidified, and may be removed 
with the point of a penknife, as a hemispherical gelatinous 
mass. The mass is quite soft and moist, so that this setting, 
or coagulation^ of a drop of blood is something very different 
from its drying. 

On the third slide, this process of coagulation will be found 
not to have taken place, the blood remaining as fluid as it was 
when it left the body. The salt, therefore, has prevented the 
coagulation of the blood. Thus this very simple investigation 
teaches that blood is composed of a nearly colorless plasma, 
in which many colored corpuscles are suspended ; that it has a 
remarkable power of coagulating; and that this coagulation 
may be prevented by artificial means, such as the addition of a 
neutral salt. 

82. The Blood Corpuscles. — If, instead of using the hand 
lens, the drop of blood on the first slide be placed under the 
microscope, the particles, or corpuscles of the blood will be 
found to be bodies with very definite characters, and of two 
kinds, called respectively the red corpuscles and the colorless 
corpuscles. The former are much more numerous than the lat- 
ter, and have a yellowish-red tinge ; while the latter, somewhat 



ITS MICROSCOPICAL ELEMENTS. 67 

larger than the red corpuscles, are, as their name implies, pale 
and devoid of coloration. 

83. Their Size, Form, and Appearance. — The corpuscles 
differ also in other and more important respects. The red corpus- 
cles are flattened circular disks, on an average g^^^^th of an inch 
in diameter, and having about one-fourth of that thickness. It 
follows that rather more than 10,000,000 of them will lie on a 
space one inch square, and that the volume of each corpuscle 
does not exceed t-2-o,o-oo!iro"iF,(roi)^^ ^^ ^ cubic inch. 





Fig. 25. Fig. 26. 

Corpuscles of Human Blood. 
Fig. 25.— Red Corpuscles: a, a corpuscle seen edgreways; &, a corpuscle in an altered 
stato, arising from pressure. A small rounded red corpuscle, such as may be 
frequently met with in the blood, is represented beside the larger discoidal ones. 
Fig. 26.— Colorless Corpuscles: a, a colorless corpuscle acted upon by diluted ace- 
' tic acid, showing its nucleus. 

The broad faces of the disks are not flat, but somewhat con- 
cave, as if they were pushed in toward one another. Hence 
the corpuscle is thinner in the middle than at the edges, and 
when viewed under the microscope, by transmitted light, looks 
clear in the middle and darker at the edges, or dark in the mid- 
dle and clear at the edges, according to circumstances. When 
the disks roll over and present their edges to the eye, on the 
other hand, they look like rods. All these varieties of appear- 
ance may be made intelligible by turning a round biscuit or a 
muffin, bodies similar in shape to the red corpuscles, in various 
ways before the eye. 

84. Structure and Changes of Form. — The red corpuscles 
are very soft, flexible, and elastic bodies, denser externally than 
in their interior, where they consist of a semifluid, or quite fluid 
matter, containing an albuminous substance icrmed globulin, in 



68 



ELEMENTARY PHYSIOLOGY. 



solution, and are reddened by their peculiar coloring matter, 
which is called hoematin. The interior substance contains no 
structure of any kind. From the density of the outer as com- 
pared with the inner substance of each corpuscle, they are, 
practically, small flattened bags, or sacs, the form of which 
may be changed by altering'the density of the plasma. Thus, 
if it be made denser by dissolving saline substances or sugar in 
it, water is drawn from the contents of the corpuscle to the 
dense plasma, and the corpuscle becomes still more flattened. 
On the other hand, if the plasma be diluted with water, the lat- 
ter forces itself into and dilutes the contents of the corpuscle, 
causing the latter to swell out, and even become spheiical ; and, 
by adding dense and weak solutions alternately, the corpuscles 
may be made to become successively spheroidal and discoidal. 
Exposure to carbonic acid gas causes the corpuscles to swell out; 
oxygen gas, on the contrary, makes them flatten. 




c 

Fig. 2T. 

Successive Fokms assumed by Colorless Corpuscles of Human Blood. 

The interval between the forms ah cd was a minute ; between d and e two minutes; 
so that the whole series of changes from a to e took five minutes. 



85. The Colorless Corpuscles are larger than the red corpus- 
cles, their average diameter being ^^th of an inch. They are 
further seen, at a glance, to differ from the red corpuscles by 
the extreme irregularity of their form, and by their tendency to 
attach themselves to the glass slide, while the red corpuscles 
float about and tumble freely over one another. 

A still more remarkable feature of the colorless corpuscles, 
than the irregularity of their form, is their irritability. The 
form of a red corpuscle is changed only by influences from 
without, such as pressure, or the like ; that of the colorless cor- 
puscle is undergoing constant alteration, as the result and ex- 



ITS MICKOSCOPICAL ELEMENTS. G9 

pression of changes taking place in its own substance. To see 
these changes well, a microscope with a magnifying power of 
five or six hundred diameters is requisite ; and even then, they 
are so gradual, that the best way to make sure of their exist- 
ence is to make a, drawing of a given colorless corpuscle at in- 
tervals of a minute or two. This is what has been done with 
the corpuscle represented in Fig. 27, in which a represents the 
form of the corpuscle when first observed ; 6, its form a minute 
afterward ; c, that at the end of the second ; d^ that at the end 
of the third ; and e, that at the end of the fifth minute. 

Careful watching of a colorless corpuscle, in fact, shows 
that every part of its surface is constantly changing — undergoing 
active contraction, or being passively dilated by the contraction 
of other parts. It exhibits contractility in its lowest and most 
primitive form. 

86. Structure and Contractility. — While they are thus 
living and active, no correct notion can be formed of the struc- 
ture of the colorless corpuscles. By diluting the blood with 
water, or still better, with water acidulated with acetic acid, the 
corpuscles are killed, and become distended, so that their real 
nature is shown. They are then seen to be spheroidal bags, or 
sacs, with very thin walls ; and to contain in their interior a 
fluid which is either clear or granular, with a spheroidal vesicu- 
lar body, which is called the nucleus (Fig. 26). It sometimes, 
though very rarely, happens that the nucleus has a red tint. 

The sac-like colorless corpuscle, with its nucleus, is what is 
called a nucleated cell. It will be observed that it is living, in a 
free state, in the plasma of tbe blood, and that the cell w^all, or 
sac, exhibits an independent contractility. In foct, except that 
it is dependent for the conditions of its existence upon the 
plasma, it might be compared to one of those simple organisms 
which are met with in stagnant water, and arc called Amabce. 

87. Their Development and Derivation.— That the red 
corpuscles are, in some way or other, derived from tlio color- 
less corpuscles may be regarded as certain ; but the stops of 
the process have not been made out with pertoct certainty. 



70 ELEMENTARY PHYSIOLOGY. 

There is very great reason, however, for believing that the red 
corpuscle is simply the nucleus of the colorless corpuscle some- 
what enlarged ; flattened from side to side ; changed, by de- 
velopment within its interior of a red coloring matter ; and set 
free by the bursting of the sac or wall of the colorless corpus- 
cle. In other words, the red corpuscle is a free nucleus. The 
origin of the colorless corpuscles themselves is not certainly 
determined ; but it is highly probable that they are constituent 
cells of the solid substance of the body which have been de- 
tached and carried into the blood, and that this process is 
largely efi'ected in what are called the ductless glands, from 
w^hence the detached cells pass, as lymph-corpuscles, directly or 
indirectly, into the blood. 

The following facts are of importance in their bearing on 
the relation between the different kinds of corpuscles: 

(a) The invertebrate animals which have true blood corpus- 
cles, possess only such as resemble the colorless corpuscles of man. 

{I) The lowest vertebrate animal, the Lancelet (Amphioxus), ' 
possesses only colorless corpuscles ; and the very young em- 
bryos of all vertebrate animals have only colorless and nucle- 
ated corpuscles. 

(c) All the vertebrated animals which lay eggs have two 
kinds of corpuscles — colorless corpuscles, like those of man, and 
large red-colored corpuscles, which are generally oval, and 
further differ from those of man in presenting a nucleus. In 
fact, they are simply the colorless corpuscles enlarged and 
colored. 

(d) All animals which suckle their young (or what are 
called mammals) have, like man, two kinds of corpuscles : color- 
less ones, and small colored corpuscles — the latter being always 
flattened, and devoid of any nucleus. They are usually circu- 
lar, but in the camel tribe they are elliptical. And it is worthy 
of remark that, in these animals, the nuclei of the colorless 
corpuscles become elliptical. 

(e) The colorless corpuscles differ much less from one an- 
other m size and form, in the vertebrate series, than the colored. 



ITS MICROSCOPICAL ELEMENTS, 7l 

The latter are smallest in the little Musk Deer, in which animal 
they are about a quarter as large as those of man. On the 
other hand, the red corpuscles are largest in the Amphibia (or 
Frogs and Salamanders), in some of which animals they are ten 
times as long as in man. 




Fig. 2S. 

Eed Coepfscles of Huma-n Blood arranged in Coherent Eolls. 

One free red corpuscle and one colorless corpuscle are seen, and tbe plasma in the 
field of view is traversed by very delicate filaments of fibrin. 

88. Red Corpuscles tend to cohere in Rolls.— As the 

blood dies, its several constituents, which have now been de- 
scribed, undergo marked changes. 

The colorless corpuscles lose their contractility, but other- 
wise undergo little alteration. They tend to cohere neither 
with one another, nor with the red corpuscles, but adhere to 
the slide on which they are placed. 

It is quite otherwise with the red corpuscles^ which at first, 
as we have seen, float about and roll, or slide, over each other 
quite freely. After a short time (the length of which varies in 
different persons, but usually amounts to tw^o or three minutes) 
they seem, as it were, to become sticky, and tend to cohere ; 
and this tendency increases until, at length, the great majority 
of them become applied face to face, so as to form long series, 
like rolls of coin. The end of one roll cohering with the sides 
of another, a network of various degrees of closeness is pro- 
duced ; the corpuscles remain thus coherent for a certain length 
of time, but eventually separate and float freely again. The 



72 ELEMENTARY PHYSIOLOGY. 

addition of a little water, or dilute acids, or saline solutions, 
will at once cause the rolls to break up. 

It is from this running of the corpuscles together into 
patches of network that the change noted above in the appear- 
ances of the layer of blood, viewed with a lens, arises. So 
long as the corpuscles are separate, the sandy appearance 
lasts ; but when they run together, the layer appears patchy or 
spotted. 

The red corpuscles rarely, if ever, all run together into rolls, 
some always remaining free in the meshes of the net. In con- 
tact with air, or if subjected to pressure, many of the red cor- 
puscles become covered with little knobs, so as to look like 
minute mulberries — an appearance which has been mistaken 
for a breaking up, or spontaneous division, of the corpuscles 
(Fig. 25, b). 

89. Blood Crystals, — There is a still more remarkable change 
which the red blood corpuscles occasionally undergo. Under 
certain circumstances, their contents, consisting of the colorless 
substance called Globulin, which fills the red blood corpuscles, 
and of their coloring matter, termed Hcematin^ separate from 
the outer shell of the corpuscles as crystals, which in man have 
the shape of prisms; in other animals take other forms. Treat- 
ment of the blood with oxygen and with carbonic acid, in sun- 
light, greatly facilitates this process, so that the easiest way to 
see these blood crystals is to expose a drop of blood to the air, 
then moisten it with water, and then, by breathing several times 
on it, supply it with carbonic acid! The color of the drop 
brightens as the crystals form in it. 

Sectiox II. — Its Physical and Chemical Properties. 

90. Coagulation. — When the layer of blood has been 
drawn ten or fifteen minutes, the plasma will be seen to be no 
longer clear. It then exhibits multitudes of extremely delicate 
filaments of a substance called Fibrin, which have been de- 
posited from it, and which traverse it in all directions, uniting 



ITS PHYSICAL AND CHEMICAL PKOPEKTIES. i{> 

with one anotlier and with the corpuscles, and binding the 
whole into a semi-solid mass. 

It is this deposition of fibrin which is the cause of the 
apparent solidification, or coagulation, of the drop upon the 
second slide ; but the phenomena of coagulation, which are of 
very great importance, cannot be properly understood until the 
behavior of the blood, when drawn in larger quantity than a 
drop, has been studied. 

91. Separation of tlie Constituents. — When, by the ordi- 
nary process of opening a vein with a lancet, a quantity of 
blood is collected into a basin, it is at first perfectly fluid ; but 
in a quarter of an hour, and sometimes in less than half that 
time, it separates into two very diflferent constituents — the one 
a clear yellowish liquid, the other a red semi-solid mass, w^hich 
lies in the liquid, and is paler in color and firmer at the surface 
than in its deeper part. 

The liquid is called the serum; the semi-solid mass the 
clot, or crassamentum. Now the clot obviously contains the 
corpuscles of the blood, bound together by some other sub- 
stance; and this last, if a small part of the clot be examined 
microscopically, will be found to be that fibrous-looking matter, 
fibrin^ which has been seen forming in the thin layer of blood. 
Thus the clot is equivalent to the corpuscles jf^Zws the fibrin of 
the plasma, while the serum is the plasma 7mnus the fibrinous 
elements which it contained. 

92. The Buffy Coat. — The corpuscles of the blood are 
slightly heavier than the plasma, and therefore, wdien the blood 
is drawn, they sink very slowly tow^ard the bottom. Hence 
the upper part of the clot contains fewer corpuscles and is 
lighter in color, than the lower part — there being fewer cor- 
puscles left in the upper layer of plasma for the fibrin to catch 
when it sets. And there are some conditions of the blood in 
which the corpuscles run together much more rapidly and in 
denser masses than usual ; so that they more readily overcome 
the resistance of the plasma to their ialling, just as feathers 
stuck together in masses fall much more rapidly through the 

4 



74 ELEMENTARY PHYSIOLOGY. 

air than the same feathers when loose. When this is the case, 
the upper stratum of plasma is quite free from red corpuscles 
before the fibrin forms in it, and consequently the uppermost 
layer of the clot is nearly white : it receives the name of the 
huffy coat. 

After the clot is formed, the fibrin shrinks and squeezes 
out much of the serum contained within its meshes ; and, other 
things being equal, it contracts the more, the fewer corpuscles 
there are in the way of its shrinking. Hence, when the buSy 
coat is formed, it usually contracts so much as to give the clot 
a cup-like upper surface. 

Thus the buffy coat is fibrin naturally separated from the 
red corpuscles ; the same separation may be effected, artificially, 
by whipping the blood with twigs as soon as it is drawn, 
until its coagulation is complete. Under these circumstances 
the fibrin will collect upon the twigs and a red fluid will be left 
behind, consisting of the serum 2^lus the red corpuscles, and 
many of the colorless ones. 

93. Influencing Conditions. — The coagulation of the blood 
is hastened, retarded, or temporarily prevented by many cir- 
cumstances. 

(a) Temperature. — A high temperature accelerates the 
coagulation of the blood; a low one retards it; and blood 
kept at the freezing-point of water will not coagulate at all. 
Blood thus kept fluid wall, however, coagulate when its tem- 
perature is raised, and blood has been thus cooled and warmed 
till near coagulation for three successive times without losing 
its coagulability. 

(h) The addition of soluble matter to the blood. — Many 
saline substances, and more especially sulphate of soda and 
common salt, added to the blood in sufficient quantity, prevent 
its coagulation; but coagulation sets in when water is added, 
so as to dilute the saline solution. 

(c) Contact with living or not-living matter, — Contact with 
not-living matter promotes the coagulation of the blood. Thus, 
blood drawn into a basin begins to coagulate first w^here it is 



ITS PHYSICAL AND CHEMICAL PROPERTIES. 7o 

ill contact with the sides of the basin; and a wire introduced 
into a living vein will become coated with fibrin, although per- 
fectly fluid blood surrounds it. 

On the other hand, direct contact with hving matter retards, 
or altogether prevents, the coagulation of the blood. Thus 
blood remains fluid for a very long time in a portion of a vein 
which is tied at each end. 

The heart of a turtle remains alive for a lengthened period 
(many hours or even days) after it is extracted from the body ; 
and, so long as it remains alive, the blood contained in it will 
not coagulate, though a portion of the same blood taken out 
of the heart will coagulate in a few minutes. 

Blood taken from the body of the turtle, and kept from 
coagulating by cold for some time, may be poured into the 
separated heart, and then will not coagulate. 

Freshly deposited fibrin acts like living matter, coagulable 
blood remaining fluid for a long time in tubes coated with such 
fibrin. 

94. Ifature of the Process of Coagulation. — The coagu- 
lation of the blood is an altogether physico-chemical process, 
dependent upon the properties of certain of the constituents of 
the plasma, apart from the vitality of that fluid. This is proved 
by the fact that if the coagulation of blood-plasma be prevented 
by cold, and it be greatly diluted, a current of carbonic acid 
gas passed through it will throw down a white substance, which 
white substance, dissolved in a weak solution of potash or soda, 
coagulates and yields a clot of true pure fibrin. It would be 
absurd to suppose that a substance which has been precipitated 
from its solution, and redissolved, still remains alive. 

There are reasons for believing that this white substance 
consists of two constituents of very similar composition which 
exist separately in living blood, and the union of which is the 
cause of the act of coagulation. These reasons may be briotly 
stated thus : — The pericardium and other serous cavities in the 
body contain a clear fluid, which has exuded from the blood- 
vessels, and contains the elements of tlio Mood without the 



76 ELEMENTARY PHYSIOLOGY. 

blood corpuscles. This fluid sometimes coagulates spon- 
taneously, as the blood-plasma would do, but very often shows 
no disposition to spontaneous coagulation. When this is the 
case, it may nevertheless be made to coagulate, and yield a 
true fibrinous clot, by adding to liglGhitUn in any of its shapes. 
This globulin is, as w^e have seen, the chief constituent of the 
-blood-corpuscles: it exists in the serum of blood which has 
coagulated, and may be precipitated therefrom, as a white 
powder, by the action of carbonic acid : it is found also in con- 
nective tissue, the cornea, lens, and humors of the eye, and in 
other fluids of the body. 

95. Globulin and Fibrinogen.^ — Globulin may be dried or 
kept in alcohol, w^ithout diminishing its power of generating 
fibrin when it is added to serous effusions. It is most active 
in a very weakly alkaline solution. Too much alkali and any 
acidity completely suspend its action. 

Thus globulin^ added under proper conditions to serous 
effusion, is a coagulator of that effusion, giving rise to the 
development of fibrin in it. 

It does so by its interaction with a substance contained in 
the serous effusion, which can be extracted by itself, and then 
plays just the same part toward a solution of globulin, as glob- 
ulin does toward its solution. This substance has been called 
fibrinogen. It is exceedingly like globulin, and may be thrown 
down from serous exudation by carbonic acid, just as globulin 
may be precipitated from the serum of the blood. When re- 
dissolved in an alkaline solution, and added to any fluid con- 
taining globulin, it acts as a coagulator of that fluid, and gives 
rise to the development of a clot of fibrin in it. In accord- 
ance with what has just been stated, serum of blood v,^hich has 
completely coagulated, may be kept in one vessel, and pericar- 
dial fluid in another, for an indefinite period, without the coag- 
ulation of either. But let them be mixed, and coagulation 
sets in. 

Thus it seems to be clear, that the coagulation of the blood, 
and the formation of fibrin, are caused primarily by the inter- 



ITS PHYSICAL AND CHEMICAL mOPEKTIES, 77 

action of two substances (or two modifications of the same sub- 
stance), globulin and fihvinogen^ the former of which exists in 
great abundance in the corpuscles of the blood, and in some 
tissues of the body ; while the latter is known at present only 
in the plasma of the blood, and the lymph, and the chyle, and 
fluids derived from them. 

96. The Physical ©ualities of the Blood. — The proverb 
that " blood is thicker than water," is literally true, as the 
blood is not only "thickened" by the corpuscles, of which it 
has been calculated that no fewer than 70,000,000,000 (eighty 
times the number of the human population of the globe) are 
contained in a cubic inch, but is rendered slightly viscid by the 
solid matters dissolved in the plasma. The blood is thus ren- 
dered heavier than water, its specific gravity being about 1055. 
In other words, twenty cubic inches of blood have about the 
same weight as twenty-one cubic inches of w^ater. The cor- 
puscles are heavier than the plasma, and their volume is usually 
somewhat less than that of the plasma. Of colorless corpus- 
cles there are usually not more than three or four for every 
thousand of red corpuscles; but the number varies very ;Tmch, 
increasing shortly after food is taken, and diminishing v:\ the 
intervals between meals. The blood is, furthermore. Lot, its 
temperature being about 100° Fahrenheit. 

97. The Chemical Composition of the Blood.— Considered 
chemically, the blood is an alkaline fluid, consisting of water, 
solid and gaseous matters. The proportions of these several con- 
stituents vary according to age, sex, and condition, but the 
following statement holds good on the average : 

In every 100 parts of blood there are TO parts of water and 
21 parts of dry solids ; in other words, the water and the solids 
of the blood stand to one another in about the same proportion 
as the nitrogen and the oxygen of the air. Roughly speaking, 
one-quarter of the blood is dry, sohd matter; three-quai-ters 
water. Of the 21 parts of dry solids, 12 {— ^ths) belong to 
the corpuscles. The remaining 9 are about two-thirds (0*7 
parts = -|ths) albumen (a substance like white of egg, coagu- 



Y8 ELEMENTARY PHYSIOLOGY. 

lating by heat), and one-tliird (.= ith of the whole solid mat- 
ter), a mixture of salhie, fatty, and saccharine matters, sundry 
products of the waste of the body, and fibrin. The quantity 
of the latter constituent is remarkably small in relation to the 
conspicuous part it plays in the act of coagulation. Healthy 
blood, in fact, yields, in coagulating, not more thau from two 
to four parts in a thousand of its weight of fibrin. 

The total quantity of gaseous matter contained in the blood 
is equal to rather less than half the volume of the blood ; that 
is to say, 100 cubic inches of blood will contain rather less 
than 50 cubic inches of gases. These gaseous matters arc 
carbonic acid, oxygen, and nitrogen ; or, in other words, the 
same gases as those which exist in the atmosphere, but in 
totally different proportions ; for whereas air contains nearly 
three-fourths nitrogen, one-fourth oxygen, and a mere trace of 
carbonic acid, the average computation of the blood gases is 
nearly two-thirds carbonic acid, rather less than one-third ox- 
ygen, and not one-tenth nitrogen. 

It is important to observe (a) that blood contains much 
more oxygen gas than could be held in solution by mere water 
at the same temperature and pressure ; {h) that this powci* of 
holding oxygen appears in some way to depend upon the cor- 
puscles, firstly, because mere serum has no greater power of 
absorbing oxygen than water has, and, secondly, because a 
solution of hasmatin absorbs oxygen very readily ; and (c) that 
somiC substances which are capable of being oxidated with 
great readiness — such as pyrogallic acid — are not affected by 
their passage through the blood. Thus it would appear that 
the oxygen is not quite free, but is held in some sort of loose 
chemical combination with a constituent of the blood contained 
in the corpuscles. 

The corpuscles differ chemically from the plasma, in con- 
taining a large proportion of the fats and phosphates, all the 
iron, and almost all the potash, of the blood ; while the plas- 
ma, on the other hand, contains by far the greater part of the 
chlorine and the soda. 



ITS PHYSICAL AND CHEMICAL PKOPEKTIES. T9 

98. Influence of Age, Sex, and Food upon the Blood. — The 

blood of adults contains a larger proportion of solid constitu- 
ents than that of children, and that of men more than that of 
women ; but the difference of sex is hardly at all exhibited by 
persons of flabby, or what is called lymphatic, constitution. 

Animal diet tends to increase the quantity of the red cor- 
puscles ; a vegetable diet and abstinence to diminish them. 
Bleeding exercises the same influence in a still more marked 
degree, the quantity of red corpuscles being diminished there- 
by in a much greater proportion than that of the other soHd 
constituents of the blood. 

99. Total auantity of Blood in the Body.— The total 
quantity of blood contained in the body varies at difi'erent 
times, and the precise ascertainment of its amount is very diffi- 
cult. It may probably be estimated, on the average, at not 
less than one-tenth of the weight of the body. 

100. Vivifying Influence of Blood over the Tissues. — 
The function of the blood is to supply nourishment to, and 
take away waste matters from, all parts of the body. It is ab- 
solutely essential to the life of every part of the body that it 
should be in such relation v^^ith a current of blood, that matters' 
can pass freely from the blood to it, and from it to the blood, 
by transudation through the walls of the vessels in which the 
blood is contained. Furthermore, this vivifying influence de- 
pends upon the corpuscles of the blood. The proof of these 
statements lies in the following experiments : If the vessels of 
a limb of a living animal be tied in such a manner as to cut 
off the supply of blood from the limb without afl'ecting it in 
any other w^ay, all the symptoms of death will set in. The 
limb will grow pale and cold, it will lose its sensibility, and 
volition will no longer have power over it ; it will stifleii, and 
eventually mortify and decompose. 

But if, even when the death stiffening has set in, the lig- 
atures are removed, and the blood is allowed to flow into the 
limb, the stiffening speedily ceases, the temperature of the part 
rises, the sensibility of the skin returns, the will regains power 



80 ELEMENTARY PHYSIOLOGY. 

over the muscles, and, in short, the part returns to its nonnal 
condition. 

If, instead of simply allowing the blood of the animal 
operated upon to flow again, such blood, deprived of its fibrin 
by whipping, but containing its corpuscles, be artificially passed 
through the vessels, it will be found as effectual a restorative as 
entire blood ; while, on the other hand, the serum (which is 
equivalent to whipped blood without its corpuscles) has no 
such effect. 

101. Transfusion of Blood. — Furthermore, it is not neces- 
sary that the blood employed should be that of the very same 
animal. Men, or dogs, bled to apparent death may be at once 
and efl'ectually revived by filling their veins with blood taken 
from another man or dog, an operation which is known by the 
name of transfusion. 

Nor is it absolutely necessary for the success of this opera- 
tion that the blood used in transfusion should belong to an 
animal of the same species. The blood of a horse will per- 
manently revive an ass, and, speaking generally, the blood of 
one animal may be replaced without injurious effects by that 
of another closely -allied species; while that of a very different 
animal will be more or less injurious, and may even cause im- 
mediate death. 

102. The Lymph, — which fills the lymphatic vessels, is, 
like the blood, an alkaline fluid, consisting of a plasma and 
corpuscles, and coagulates by the separation of fibrin from the 
plasma. The lymph diff*ers from the blood in its corpuscles 
being all of the colorless kind, and in the very small proportion 
of its solid constituents, w^hich amount to only about five per 
cent. Lymph may, in fact, be regarded as blood minus its red 
corpuscles, and diluted with water, so as to be somewhat less 
dense than the serum of blood, which contains about eight per 
cent, of solid matters. 

A quantity of fluid equal to that of the blood is probably 
poured into the blood, daily, from the lymphatic system. 
This fluid is in great measure the mere overflow of the blood 



ARTERIAL AND VENOUS BLOOD. 81 

itself — plasma which has exuded from the capillaries into the 
tissues, and which has not been taken up again into the venous 
current ; the rest is due to the absorption of chyle from the 
alimentary canal. 



CHAPTER V. 

OP RESPIRATION. 

Section I. — Arterial and Venous Blood, 

103, High Complexity of the Blood.— The blood, the 
general nature and properties of which have been described in 
the preceding chapter, is the highly complex product, not of 
any one organ or constituent of the body, but of all. Many 
of its features are doubtless given to it by its intrinsic and 
proper structural elements, the corpuscles; but the general 
character of the blood is also profoundly aflected by the cir- 
cumstance that every other part of the body takes something 
from the blood and pours something into it. The blood may 
be compared to a river, the nature of the contents of which is 
largely determined by that of the head-waters, and that of the 
animals which swim in it; but which is also very much affected 
by the soil over which it flows, the water-w^eeds which cover 
its banks, and by affluents from distant regions — by irrigation 
works which are supplied from it, and by drain -pipes which 
flow into it. 

104. Blood rendered venous in the Capillaries. — One 
of the most remarkable and important of the changes effected 
in the blood is that which results, in most pai-ts of the body, 
from its simply passing through capillaries, or, in other words, 
through vessels, the walls of which are thin enough to perm it a 
free exchange between the blood and the fluids which ponnoate 
the adjacent tissues. 

Thus, if blood be taken from an artery supplying a limb, it 



82 ELEMENTARY PHYSIOLOGY. 

will be found to Lave a bright scarlet color; wliile blood drawn 
at tbe same time from the vein of the limb, will be of a pur- 
plish hue, so dark that it is commonly called " black blood." 
And as this contrast is met with in the contents of the arteries 
and veins in general (except the pulmonary arterj^ and veins), 
the scarlet blood is commonly known as arterial^ and the 
black blood as venous. 

This power of converting arterial into venous blood re- 
mains in most parts of the body so long as life persists. Tlius, 
if a limb be cut off and scarlet blood be forced into its arteries 
by a syringe, it will issue from the veins as black blood so long 
as the limb exhibits signs of persistent vitality ; and when 
these disappear the blood will no longer be changed. 

105. Difference between Arterial and Venous Blood.— 
When specimens of venous cind of arterial blood are subjected 
to chemical examination, most of the differences between them 
are found to be very small and inconstant. As a rule, there is 
lather more water in arterial blood, and rather more fatty mat- 
ter. But the gaseous contents of the two kinds of blood differ 
widely in the proportion which the carbonic acid gas bears to 
the oxygen, there being a smaller quantity of oxygen and a 
greater quantity of carbonic acid, in venous than in arterial blood. 

And it may be experimentally demonstrated that this dif- 
ference in the gaseous contents is the only essential difference 
between venous and arterial blood. For if arterial blood be 
shaken up with carbonic acid so as to be thoroughly saturated 
with that gas, it loses oxygen, gains carbonic acid, and acquires 
the hue and proportion of venous blood ; while, if venous blood 
be similarly treated with oxygen, it gains oxygen, loses carbonic 
acid, and takes on the color and properties of arterial blood. 
Furthermore, the same result is attained, though more slowly, 
if the blood, in either case, be received into a bladder, and then 
placed in the carbonic acid or oxygen gas; the thin moist ani- 
mal membrane allowing the change to be effected with peifect 
ease, and offering no serious impediment to the passage of either 
gas. 



ARTEKIAL AND VENOUS BLOOD. 83 

106. Diffusion of Gases. — The physico-chemical processes 
involved in the exchange of carbonic acid for oxygen when 
venous is converted into arterial blood, or the reverse, in the 
cases mentioned above, are not thoroughly understood, and are 
probably somewhat complex. 

It is known (a) that gases, mechanically held by a fluid in 
a given proportion, tend to diffuse into any atmosphere to 
whicli they are exposed, until tbey occupy that atmosphere in 
corresponding proportions ; and (b) that gases, separated by a 
dry porous partition, or simply in contact, diffuse into one an- 
other with a rapidity Vv^hicb is inversely proportioned to the 
square roots of their densities. 

Now, a knowledge of these physical principles does, in a 
rough way, lead us to see how the gases, contained in the blood, 
may effect an exchange with those in the air, whether the blood 
be freely exposed, or enclosed in a membrane. But the appli- 
cation of these principles gives no more than this sort of gen- 
eral insight, seeing that, in the first place, the gases of the blood 
arc not held merely mechanically in it; and, secondly, that 
when arterialization takes place through the walls of a bladder, 
or any other thin animal membrane, the matter is still further 
complicated by the circumstance that moisture dissolves car- 
bonic acid far more freely than it will oxygen, and hence that 
the wet bladder has a very different action upon carbonic acid 
from that which it has upon oxygen. Thus a moist bladder, 
partially filled with oxygen and suspended in carbonic acid gas, 
becomes rapidly distended in consequence of the carbonic acid 
gas passing into it with much greater rapidity than the oxygen 
passes out. 

107. Cause of the Change of Color in Blood.— The cause 
of the change of color in the blood — of its darkening when ex- 
posed to carbonic acid, and its brightening when under the 
influence of oxygen, is not thoroughly understood. There is 
reason to think, however, that the red corpuscles are rendered 
somewhat flatter by oxygen gas, while they are distended by 
the action of carbonic acid. Under the former circumstances 



84 ELEMENTARY PHYSIOLOGY. 

they may, not improbably, reflect the light more strongly, so 
as to give a more distinct coloration to the blood ; while, un- 
der the latter, they may transmit more light and so allow the 
blood to appear darker and duller. 

108. Conditions of its Chemical Changes. — Whatever may 
be their explanation, however, the facts are certain, (l) that 
arterial blood, separated by only a thin membrane from car- 
bonic acid, or from a fluid containing a greater amount of 
carbonic acid than itself, becomes venous ; and (2) that venous 
blood, separated by only a thin membrane from oxygen, or a 
fluid containing a greater proportion of free oxygen than itself, 
becomes arterial. 

In these facts lies the explanation of the conversion of 
scarlet blood into dark blood as it passes through the capil- 
laries of the body, for the latter are bathed by the juices of 
the tissues which contain carbonic acid, the product of their 
waste and combustion, in excess. On the other hand, if we 
seek for the explanation of the conversion of the dark blood in 
the veins into the scarlet blood of the arteries, v/e find, 1st, 
that the blood remains dark in the right auricle, the right ven- 
tricle, and the pulmonary artery ; 2d, that it is scarlet not only in 
the aorta, but in the left ventricle, the left auricle, and the pul- 
monary veins. 

Obviously, then, the change from venous to arterial takes 
place in the pulmonary capillaries, for these are the sole chan- 
nels of communication between the pulmonary arteries and the 
pulmonary veins. 

Section II. — The Lungs and their Office. 

109. The Essence-nature of Respiration.— But what are 
the physical conditions to which the blood is exposed in the 
pulmonary capillaries ? 

These vessels are very wide, thin walled, and closely set, so 
as to form a network with very small meshes, which is con- 
tained in the substance of an extremely thin membrane. This 



THE LUNGS AND THEIR OFFICE. 



85 



membrane is in contact witli the air, so that the blood in each 
capillary of the lung is separated from the air by only a deli- 
cate pellicle formed by its own wall and the lung membrane. 
Hence an exchange very readily takes place between the blood 
and the air ; the latter gaining moisture and carbonic acid, and 
losing oxygen. 

This is the essential step in respiration ; that it really 
takes place may be demonstrated very readily, by the experi- 
ment described in the first chapter, in which air expired was 
proved to differ from air inspired, by containing more heat, 
more water, more carbonic acid, and less oxygen; or, on the 
other hand, by putting a ligature on the windpipe of a living 
animal so as to prevent air from passing into or out of the 
lungs, and then examining the contents of the heart and great 
vessels. Venous blood will be found on both sides of the 




Back View of the Neck and Thorax of a Hfman Subject from vrmcn 
THE Vertebral Column and wuole Posterior Wall of tue Chest 15 sup- 
posed TO BE REMOVED. 

31. mouth; Gl. glottis; TV. trachea; L.L. left h\r\g\ JR.L. right liin?; Br. bronchus; 
P. A. pulmonary artery; P.V. pulmonary veins; Ao. aorta, D. diapliragm; //. 
heart; V.C.I, vena cava inferior. 



86 ELEMENTARY PHYSIOLOGY. 

heart, and in the pulmonary veins and aorta, as much as in the 
vena cava and puhnonary artery. 

But though the passage of carbonic acid gas and hot watery 
vapor out of the blood, and of oxygen into it, is the essence 
of the respiratory process — and thus a membrane with blood 
on one side, and air on the other, is all that is absolutely neces- 
sary to effect the purification of the blood — yet the accumula- 
tion of carbonic acid is so rapid, and the need for oxygen so 
incessant in all parts of the human body, that the former could 
not be cleared away, nor the latter supplied, with adequate 
rapidity, without the aid of extensive and complicated acces- 
sary machinery — the arrangement and working of which must 
next be carefully studied. 

110. Mechanism of Respiration. — The back of the mouth 
or pharynx communicates by two channels with the external 
air. One of these is formed by the nasal passages, which can- 
not be closed by any muscular apparatus of their own ; the 
other is presented by the mouth, which can be shut or opened 
at will. Immediately behind the tongue, at the lower and 
front part of the pharynx, is an apertnre — the glottis — capable 
of being closed by a sort of lid — the epiglottis — which covers 
it, or by the shutting together of its side boundaries, formed 
by the so-called vocal chords. The glottis opens into a cham- 
ber with caililaginous walls — the larynx ; and leading from the 
larynx downward along the front part of the throat, where it 
may be very readily felt, is the trachea^ or windpipe. If this 
last be handled through the skin, it will be found to be firm 
and resisting. Its walls are, in fact, strengthened by a series 
of cartilaginous hoops, which hoops are incomplete behind, 
their ends being united only by muscle and membrane, where 
the trachea comes into contact with the gullet or oesophagus. 
The trachea passes into the thorax, and then divides into two 
branches, a right and a left, which are termed the bronchi. 
Each bronchus enters the lung of its own side and then divides 
into a great number of smaller branches, which are called 
the bronchial tubes. As these diminish in size, the cartilages * 



THE LUNGS AND THEIR OFFICE. 



87 



which are continued all through the bronchi, and their large 
ramifications, become smaller and eventually disappear, so that 
the smallest bronchial tubes have wholly muscular and mem- 
branous walls. Thus, while the trachea and bronchi are kept 
permanently open and pervious to air, the smaller bronchial 
tubes may be almost closed by the contraction of their mus- 
cular walls. 



Fig. 80. 



Fig. 81. 




Fig. 32. 

Fio. 80.— Two air-cells (b) with the ultimate bronchial tube (a) which opens into 

them. 
Fig. 81. — A section through the walls (a) of several air-cells with their epithelium (5). 
Fig. 82. — The capillaries of the air-ceils. 



The finer bronchial tubes end at leno-th in clonorated dila- 
tations, about jV^h of an inch in diameter on the average, 
which are called the air-cells, and which have sacculated walls. 
The very thin walls which separate these air-cells are supported 
by much delicate and highly elastic tissue, and carry the wide 
and close-set capillaries into which the pulmonary artery pours 
its blood. Thus, the blood contained in these capillaries is 



88 ELEMENTARY PHYSIOLOGY. 

exposed on botli sides to the air — ^being separated from the air- 
cell on either hand only by the very delicate pellicle which 
forms the wall of the capillary, and the Hning of the air-sac. 

111. The Provision for the Renewal of Air. — Hence no 
conditions can be more favorable to a ready exchange between 
the gaseous contents of the blood and those of the air in the 
air-cells, than the arrangements which obtain in the pulmonary 
capillaries ; and, thus far, the structure of the lung fully enables 
us to understand how it is that the large quantity of blood 
poured through the pulmonary circulation is enabled to be ex- 
posed in very thin streams, over a large surface, to the air. 
But this very circumstance would only render the extraction 
of the oxygen from the pulmonary air, and its saturation with 
carbonic acid, a very speedy and complete process, if it were 
not for the special arrangements by which a certain quantity 
of this air is incessantly removed and replaced by fresh air. 

112. Inspiration and Expiration. — If an adult man, 
breathing calmly in the sitting position, be watched, the respi- 
ratory act will be observed to be repeated thirteen or fourteen 
times every minute. Each act consists of certain components 
which succeed one another in a regular rhythmical order. 
First, the breath is drawn in, or inspired ; immediately after- 
ward it is driven out, or expired ; and these successive acts of 
inspiration and expiration are followed by a brief pause. Thus, 
just as in the rhythm of the heart we have auricular systole, 
ventricular systole, pause ; so in similar order in the chest, in- 
spiration, expiration, and pause succeed one another. At each 
inspiration in an adult w^ell-grown man about thirty cubic 
inches of air are inspired, and at each expiration the same, or 
a slightly smaller, volume (allowing for the increase of tem- 
perature of the air so expired). 

113. Differences between Inspired and Expired Air. — 
The expired air differs from the air inspired in the following 
particulars : 

(a) Whatever the temperature of the external air, that ex- 
pired is nearly as hot as the blood, or between 90° and 100°. 



THE LUJSGS AND THEIR OFFICE. 89 

(6) However dry the external air may be, that expired is 
quite, or nearly, saturated with watery vapor. 

(c) Though ordinary air contains nearly 2,100 parts of oxy- 
o-en, and 7,900 of nitrogen, with not more than three parts of 
carbonic acid, in 10,000 parts, expired air contains about 470 
parts of carbonic acid, and only between 1,500 and 1,600 parts 
of oxygen, while the quantity of nitrogen suflfers little or no 
change. Speaking roughly, air which has been breathed once 
has gained five per cent, of carbonic acid, and lost five per cent, 
of oxygen. 

The expired air contains, in addition, a greater or less 
quantity of animal matter of a highly decomposable character. 

(d) Very close analysis of the expired air shows, firstly, 
that the quantity of oxygen which disappears is always slightly 
in excess of the quantity of carbonic acid supplied; and 
secondly, that the nitrogen is variable— that in the expired air 
being sometimes slightly in excess of, sometimes slightly less 
than, that in the inspired air, and sometimes remaining sta- 
tionary. 

114. The Amount of Work done by the Lungs. — Three 
hundred and fifty to four hundred cubic feet of air are thus passed 
through the lungs of an adult man taking little or no exercise, 
in the course of twenty-four hours, and are charged with car- 
bonic acid, and deprived of oxygen to the extent of nearly five 
per cent, which amounts to about eighteen cubic feet of the 
one gas taken in, and of the other given out. Thus, if a man 
be shut up in a close room, having the form of a cube seven 
feet in the side, every particle of air in that room will have 
passed through his lungs in twent3^-four hours, and a fourth 
of the oxygen it contains will be replaced by carbonic acid. 

The quantity of carbon eliminated in the twenty-four hours 
is pretty clearly represented by a piece of pure charcoal weigh- 
ino: eio^ht ounces. 

The quantity of water given off from the lungs in the 
twenty -four hours varies very much, but may be taken on the 
average as rather more than half a pint, or about nine ounces. 



90 ELEMENTARY PHYSIOLOGY. 

It may fall below this amount, or increase to double or treble 
the quantity. 

Section III. — The Respiratory Mechanism. 

115. Mechanism of the Respiratory Movements. — The 

mechanical arrangements by which the respiratory movements 
essential to the removal of the great mass of effete matters, and 
the importation of the large quantity of oxygen indicated, are 
effected, are to be found in — (a) the elasticity of the lungs. (6) 
The mobility of the sides and bottom of the thoracic cavity in 
which the lungs are contained. 

(a) The thorax may be regarded as a completely shut con- 
ical box, with the small end turned upward, the back of the 
box being formed by the spinal column, the sides by the ribs, 
the front by the breast-bone, the bottom by the diaphragm, 
and the top by the root of the neck (Fig. 29). 

The two lungs occupy almost all the cavity of this box 
which is not taken up by the heart. Each is enclosed in its 
serous membrane, the pleura. So long as the walls of the 
thorax are entire, the cavity of each pleura is practically oblit- 
erated, that layer of the pleura which covers the lung being in 
close contact with that which lines the wall of the chest ; but 
if a small opening be made into the pleura, the lung at once 
shrinks to a comparatively small size, and thus develops a 
great cavity between the two layers of the pleura. If a pipe 
be now fitted into the bronchus, and air blown through it, the 
lung is very readily distended to its full size ; but, on being 
left to itself, collapses, the air being driven out again with 
some force. The abundant elastic tissue of the walls of 
the air-cells is, in fact, so disposed as to be greatly stretched 
when the lungs are full ; and, when the distending cause is 
removed, this elasticity comes into play and drives the greater 
part of the air out again. 

The lungs are kept distended m the dead subject, so long 
as the walls of the chest are entire, by the pressure of the 



THE RESPIRATORY MECHANISM. 



91 



atmosphere. For though the elastic tissue is all the while 
jDuUing, as it were, at the layer of pleura which covers the 
lung, and attempting to separate it from that which lines the 
chest, it cannot do so Avithout developing a vacuum between 
these two layers. To effect this, the elastic tissue must pull 
with a force of more than that of the external air, or fifteen 
pounds to the square inch, an effort far beyond its powers, 
which do not equal more than one-fourth of a pound on the 
square inch. But the moment a hole is made in the pleura, 
the atmospheric pressure inside the lung is equalized by that 
outside it, and the elastic tissue, freed from its opponent, ex- 
erts its full power on the lung. 

116. Walls of tlie Bronchial Tubes—Cilia. — The lungs 
are elastic, whether alive or dead. During life the air which 
they contain may be further affected by the contractility of 
the muscular walls of the bronchial tubes. If water is poured 
into the lungs of a recently -killed animal, and a series of elec- 
tric shocks is then sent through the bronchial tubes, the latter 
contract, and the water is forced out. Lastly, daring life a 
further source of motion in the bronchial tubes is provided by 
the cilia — minute filaments attached to the epithelium of the 
tubes, which incessantly vibrate backward and forward, and 




Fig. S3. 



Fig. 84. 



Fig. 83.— (^. 7.) External intercostnl muselos. 

Fig:. 84.— (7. 7.) Internal intereostal muscles. The chest is supposed to be di- 
vided vertically through the middle of the breast-bone {St.) and back-bone { V. C.) 



ELEMENTARY PHYSIOLOGY. 



work in such a manner as to sweep liquid and solid matters 
outward, or toward the trachea. 

117. Movements cf the Chest-Walls.— (5) The ribs arc 
attached to the spine, so as to be freelj^ movable upon it ; but, 
when left to themselves, they take a position w^hich is inclined 
obliquely downward and forward.^ Two sets of muscles, called 
intercosials^ pass between the successive pairs of ribs on each 
side. The outer set, called external intercostals, run from the 
rib above obliquely downw^ard and forward to the rib below. 
The other set, internal intercostals, cross these in direction passing 
from the rib above, downward and backward to the rib below. 

The action of these muscles is somewhat puzzling at first, 
but is readily understood if the principle that, when a muscle 
contracts, it tends to make the distance between its two ends as 

rt as possible, be borne in mind. Let a and 6, Fig. 35, be 




Fig. 35. 



Fig. 3G. 



Fig. 3T. 



Fig. 35, Models illustratinor the action of the external and internal intercostal 
muscles. Fig. 36, inspiratory elevation. Fig. 37, expiratory depression. 

two parallel bars, movable by their ends upon the upright c, 
which may be regarded as at the back of the apparatus, then a 
line directed from a; to y will be inclined downward and for- 
ward, and one from tv to z will be directed downward and 
backward. Now, it is obvious that there is one position of the 

* I purposely neglect the consideration of the cartilages of the ribs in order not to 
complicate the question unnecessarily. 



THE RESPIRATORY MECHANISM. 93 

rods, and one only, in which the points x and y are at the 
shortest possible distance, and one position only in which the 
points vj and z are at the shortest possible distance ; and these 
are, for x and y the position Fig. 36, and for iv and z the position 
Fig. 37. These positions are respectively such that the points 
:r, y, and w^ z^ are at the ends of a straight line perpendicular 
to both rods. 

Thus, to bring x and y into this position, the parallel rods 
in Fig. 35 must move upward ; and to bring w and z into it, 
they must move in the opposite way. 

If the simple apparatus just described be made of wood, 
hooks being placed at the points ar, y, and w^ z ; and an elastic 
band, as long when left to itself as the shortest distance be- 
tween these points, be provided with eyes which can be readily 
put on to or taken off these hooks: it will be found that when 
the bars are in the horizontal position Fig. 35, the elasticity 
of the band hooked on to x and y will bring them up into the 
position in Fig. 36 ; while, if hooked on to w and 2, it will 
force them down into the position shown in Fig. 37. 

Substitute the contractility of the external and internal 
intercostal muscles for the elasticity of the band, and it will 
precisely exemplify their action ; and it is thus proved that the 
external intercostals raise, and the internal intercostals depress, 
the bony ribs. 

118. The Diaphragm — is a great partition situated be- 
tween the thorax and the abdomen, and always concave to the 
latter and convex to the former. From its middle, which is 
tendinous, muscular fibres extend downward and outward to 
the ribs, and two, especially strong, masses, which are called 
ihe pillars of the diaphragm, io the spinal column. AVhcn 
these muscular fibres contract, therefore, they tend to make 
the diaphragm flatter, and to increase the capacity of the 
thorax at the expense of that of the abdomen, by thrusting 
down the bottom of the thoracic box. Fig. 38. 

119. Action of Diiferent Parts compared.— Let us now 
consider what would be the result of the action of the parts 



94 ELEMENTARY PHYSIOLOGY. 

of the respiratory apparatus, which have been described, if the 
diaphragm alone should begin to contract at regular intervals. 
When it contracts it increases the vertical dimensions of 
the thoracic cavity, and tends to pull away the lining of the 
bottom of the thoracic box from that which covers the base of 




Fig. 3S. 

Toe Diaphragm viewed from the lower or abdominal side. 

V. C. /., the vena cava inferior; (E., the oesophagus; Ao., the aorta; Th. /)., the 
thoracic duct, cut where they pass through the diaphragm, the broad white tendinous 
middle of which is easily distinguished from the radiating muscular fibres which pass 
down to the ribs and into the pillars in front of the vertebra?. 

the lungs ; but the air immediately rushing in at the trachea, 
proportionately increases the distension of the lungs, and pre- 
vents the formation of any vacuum between the two pleura) at 
this point. When the diaphragm ceases to contract, so much 
of the elasticity of the lungs as was neutralized by the contrac- 
tion of the diaphragm, comes into play, and the extra air taken 
in is driven out again. We have, in short, an Inspiration and 
an Expiration. 

Suppose on the other hand that, the diaphragm being qui- 
escent, the external intercostal muscles contract. The ribs 
will be raised from their oblique position, the antero-posterior 
dimensions of the thoracic cavity will be increased, and the 
lungs will be distended as before to balance the enlargement. 



INSPIRATION AND EXPIRATION. 95 

If now the external intercostals relax, the action of gravity 
upon the ribs, and the elasticity of the lungs, will alone suffice 
to bring back the ribs to their previous positions and to drive 
out the extra air; but this expiratory action may be greatly 
aided by the contraction of the internal intercostals. 

Section IV. — Inspiration and Expiration, 

120. Accessory Muscles. — Thus it appears that we may have 
either diaphragmatic respiration or costal respiration. As a gen- 
eral rule, however, not only do the two forms of respiration coin- 
cide and aid one another — the contraction of the diaphragm tak- 
ing place at the same time with that of the external intercostals, 
and its relaxation with the contraction of the internal inter- 
costals — but sundry other accessory agencies come into play. 
Thus, the muscles which connect the ribs with parts of the 
spine above them, and with the shoulder, may, more or less 
extensively, assist inspiration; while those which connect the 
ribs and breastbone with the pelvis and form the front and 
side walls of the abdomen, are powerful aids to expiration. In 
fact, they assist expiration in two ways : first, directly, by pull- 
ing down the ribs ; and next, indirectly, by pressing the vis- 
cera of the abdomen upward against the under surface of the 
diaphragm, and so driving the floor of the thorax upward. 

It is for this reason that, whenever a violent expiratory effort 
is made, the walls of the abdomen are obviously flattened and 
driven toward the spine, the body being at the same time bent 
forward. 

In taking a deep inspiration, on the other hand, the walls 
of the abdomen are relaxed and become convex, the viscera 
being driven against them by the descent of the abdomen — the 
spine is straightened, the head thrown back, and the shoulders 
outward, so as to aflbrd the greatest mechanical advantage to nil 
the muscles which can elevate the ribs. 

121. How Respiration differs in the two Sexes.— It is 
a remarkable circumstance that the mechanism of respiration 



96 



ELEMENTAKY PHYSIOLOGY. 



is somewhat different in the two sexes. In men, the diaphragm 
takes the larger share m the process, the upper ribs moving 
comparatively little ; in women, the reverse is the case, the 
respiratory act being largely costal. 

Sighing is a deep and prolonged inspiration. " Snifting" is 
a more rapid inspiratory act in wliich the month is kept shut, 
and the air made to pass through the nose. 

Coughing is a violent expiratory act in which, a deep in- 
spiration being tirst taken, the glottis is closed and then burst 
open by the violent compression of the lungs by the expiratory 
muscles, the diaphragm being relaxed and the air driven 
through the mouth. In sneezing, on the contrary, the cavity 
of the mouth is shut off and the air forced through the nasal 
passages. 





Fig. 89. Fig. 40. 

Diagrammatic Sections of the Body in 

Fig. 39, inspiration ; Fig. 40, expiration : Tr, trachea : St. sternum ; D. diaphragm i 
Af}. abdominal walls. The shading indicates the stationary air. 



INSPIRATION AND EXPIRATION. 97 

122. Residual, Supplemental, and Tidal Air. — It thus 
appears that the thorax, the lungs, and the trachea constitute 
a sort of bellows without a valve, in which the thorax and the 
lungs represent the body of the bellows, while the trachea is 
the pipe ; and the effect of the respiratory movements is just 
the same as that of the approximation, and separation of the 
handles of the bellows, viz., to drive out and draw in the air 
through the pipe. There is, however, one difference between 
the bellows and the respiratory apparatus, of great importance 
in the theory of respiration, though frequently overlooked, and 
that is, that the sides of the bellows can be brought close to- 
gether so as to force out all, or nearly all the air which they 
contain ; while the walls of the chest, when approximated as 
much as possible, still enclose a very considerable cavity 
(Fig. 40) ; so that, even after the most violent expiratory effort, 
a very large quantity of air is left in the lungs. 

The amount of this air which cannot be got rid of, and is 
called Residual air, is, on the average, from 75 to 100 cubic 
inches. 

About as much more in addition to this remains in the 
chest after an ordinary expiration, and is called Supplemental 
air. 

In ordinary breathing, 20 to 30 cubic inches of what is con- 
veniently called Tidal air pass in and out. It follows that, after 
an ordinary inspiration, 100 + 100 + 30 = 230 cubic inches, 
may be contained in the lungs. By taking the deepest possi- 
ble inspiration, another 100 cubic inclies, called Complemental 
air, may be added. 

123. The Stationary Air plays the part of a Middle- 
man. — It follows from these data that the lungs, after an ordi- 
nary inspiration, contain about 230 cubic inches of air, and 
that only about one-seventh to one-eighth of this amount is 
breathed out and taken in again at the next inspiration. Apart 
from the circumstance, then, that the fresh air inspired has to 
fill the cavities of the hinder part of the mouth, and the trachea, 
and the bronchi, if the lungs were mere bags fixed to the ends 



98 ELEMENTARY PHYSIOLOGY. 

of the bronchi, the insph-ed air could only occupy that one- 
fourteenth to one-sixteenth of the capacity of each nearest the 
bronchi, to be driven out again at the next expiration. But 
as the bronchi branch out into a prodigious number of bron- 
chial tubes, the inspired air can only penetrate for a certain dis- 
tance alono* these, and can never reach the air-cells at all. 

Thus the Residual and Supplemental air taken together are, 
under ordinary circumstances, stationary — that is to say, the 
air comprehended under these names merely shifts its outer 
limit in the bronchial tubes, as the chest dilates and contracts, 
without leaving the lungs; the tidal air, alone, being that 
which leaves the lungs and is renewed in ordinary respiration. 

It is obvious, therefore, that the business of respiration is 
essentially transacted by the stationary air, which plays the 
part of a middle-man between the two parties — the blood and 
the fresh tidal air — who desire to exchange their commodities, 
carbonic acid for oxygen, and oxygen for carbonic acid. 

Now there is nothing interposed between the fresh tidal air 
and the stationary air; they are aeriform fluids, in complete 
contact and continuity, and hence the exchange between them 
must take place according to the ordinary laws of gaseous dif- 
fusion. 

124. Composition of the Stationary Air. — Thus, the 
stationary air in the air-cells gives up oxygen to the blood, and 
takes carbonic acid from it, though the exact mode in which 
the change is effected is not thoroughly understood. By this 
process it becomes loaded with carbonic acid, and deficient in 
oxygen, though to what precise extent is not known. But 
there must be a very much greater excess of the one, and defi- 
ciency of the other, than is exhibited by inspired air, seeing 
that the latter acquires its composition by diffusion in the short 
space of time (four to five seconds) during which it is in con- 
tact with the stationary air. 

In accordance with these facts, it is found that the air ex- 
pired during the first half of an expiration contains less car- 
bonic acid than that expired during the second half. Further, 



INSPIRATION AND EXPIRATION. 99 

when the frequency of respiration is increased without altering 
the volume of each inspiration, though the percentage of car- 
bonic acid in each inspiration is diminished, it is not diminished 
in the same ratio as that in which the number of inspirations 
increases ; and hence more carbonic acid is got rid of in a given 
time. 

Thus, if the number of inspirations per minute is increased 
from fifteen to thirty, the percentage of carbonic acid evolved 
in the second case remains more than half what it was in the 
first case, and hence the total evolution is greater. 

125. Nervous System controls Respiration. — Of the 
various mechanical aids to the respiratory process, the nature 
and working of which have now been described, one, the elas- 
ticity of the lungs, is of the nature of a dead, constant force. 
The action of the rest of the apparatus is imder the control of 
the nervous system, and varies from time to time. 

As the nasal passages cannot be closed by their own action, 
air has always free access to the pharynx, but the glottis, or 
entrance to the windpipe, is completely under the control of 
the nervous system — the smallest irritation about the mucous 
membrane in its neighborhood being conveyed, by its nerves, 
to that part of the cerebro-spinal axis which is called the me- 
dulla oblongata. The medulla oblongata, thus stimulated, gives 
rise, by a process which will be explained hereafter, termed 
rejlex action^ to the contraction of the muscles which close the 
glottis, and commonly, at the same time, to a violent contrac- 
tion of the expiratory muscles, producing a " cough." 

The muscular fibres of the smaller bronchial tubes, no less 
than the respiratory pump itself, formed by the walls and floor 
of the thorax, are under the complete control of the nerves 
which supply the muscles, and which are brought into action 
in consequence of impressions conveyed by the pneumogastric 
and other nerves. 

126. Respiration and Circulation compared. — From what 
has been said, it is obvious that there are many analogies be- 
tween the circulatory and the respiratorv apparatus. Each 



100 ELEMENTARY PHYSIOLOGY. 

consists essentially of a kind of pump whicli distributes a fluid 
(aeriform in the one case, liquid in the other) through a series 
of ramified distributing tubes to a system of cavities (capilla- 
ries or air-cells), the volume of the contents of w hich is greater 
than that of the tubes. 

In each, the pump is the cause of motion of the fluid, but 
that motion may be regulated, locally, by the contraction or 
relaxation of the muscular fibres contained in the walls of the 
distributing tubes. But, while the rhythmic movement of the 
heart depends upon a nervous apparatus placed within itself, 
that of the respiratory apparatus results mainly from the opera- 
tion of a nervous centre lodged in the medulla oblongata. 

Section V. — Effects of Respiration. 

127. Their Secondary Phenomena.— As there are certain 
secondary phenomena which accompany, and are explained by, 
the action of the heart, so there are secondary phenomena 
which are similarly related to the working of the respiratory- 
apparatus. These are — (1) the respiratory sounds, and (2) the 
eflfect of the inspiratory and expiratory movements upon the 
circulation. 

128. The Respiratory Murmurs. — The respiratory sounds^ 
or murmurs^ are audible when the ear is applied to any part of 
the chest which covers one or other of the lungs. They ac- 
company inspiration and expiration, and very much resemble 
the sounds produced by breathing through the mouth, when 
the lips are so applied together as to leave a small interval. 
Over the bronchi the sounds are louder than over the general 
surface. It would appear that these sounds are produced by 
the motion of the air along the air-passages. 

129. Inspiration assists the Circulation. — In conse- 
quence of the elasticity of the lungs, a certain force must be 
expended in distending them, and this force is found exper- 
imentally to become greater and greater the more the lung is 
extended; just as in stretching apiece of india-rubber more 



EFFECTS OF RESPIRATION. 101 

force is required to stretcli it a good deal, than is needed to 
stretch it only a little. Hence, when inspiration takes place, 
and the lungs are distended with air, the heart and the great 
vessels in the chest are subjected to a less pressure than are 
the blood-vessels of the rest of the body. 

For the pressure of the air contained in the lungs is ex- 
actly the same as that exerted by the atmosphere upon the 
surface of the body ; that is to say, fifteen pounds on the 
square inch. But a certain amount of this pressure exerted by 
the air in the lungs is counterbalanced by the elasticity of the 
distended lungs. Say that in a given condition of inspiration 
a pound pressure on the square inch is needed to overcome 
this elasticity, then there will be only fourteen pounds' pres- 
sure on every square inch of the heart and great vessels. And 
hence the pressure on the blood in these vessels will be one 
pound per square inch less than that on the veins and arteries 
of the rest of the body. If there were no aortic, or pulmo- 
nary, valves, and if the composition of the vessels, and the 
pressure upon the blood in them, were everywhere the same, 
the result of this excess of pressure on the surface would be, 
to drive all the blood from the arteries and veins of the rest of 
the body into the heart and great vessels contained in the 
thorax. And thus the diminution of the pressure upon the 
thoracic blood cavities produced by inspiration, would prac- 
tically suck the blood from all parts of the body toward the 
thorax. But the suction thus exerted, while it hastened the 
flow of blood to the heart in the veins, would equally oppose 
the flow from the heart to the arteries, and the two efl"ects 
would balance one another. 

130. Tlnequal Pressures facilitate the Circulation. — As 
a matter of fact, however, we know — 

(1.) That the blood in the arteries is constantly under a 
very considerable pressure, while that of the veins is under little 
or no pressure. 

(2.) That the walls of the arteries are strong and elastic, 
while those of the veins are weak and flabby. 



102 ELEMENTARY PHYSIOLOGY. 

(3.) That tlie veins have valves opening toward the heart : 
and that, during the diastole, there is no resistance of any 
moment to the free passage of blood into the heart: while on 
the other hand, the cavity of the arteries is shut off from that 
of the ventricle during the diastole, by the closure of the semi- 
lunar valves. 

Hence it follows that equal pressures applied to the surface 
of the veins and to that of the arteries must produce very dif- 
ferent effects. In the veins the pressure is something which 
did not exist before ; and, partly from the presence of valves, 
partly from the absence of resistance in the heart, partly from 
the presence of resistance in the capillaries, it all tends to ac- 
celerate the flow of blood toward the heart. In the arteries, 
on the other hand, the pressure is only a fractional addition to 
that which existed before ; so that during the systole it only 
makes a comparatively small addition to the resistance which 
has to be overcome by the ventricle ; and during the diastole, 
it superadds itself to the elasticity of the arterial walls in driv- 
ing the blood onv/ard toward the capillaries, inasmuch as all 
progress in the opposite direction is stopped by the semilunar 
valves. 

It is, therefore, clear that the inspiratory movement, on the 
whole, helps the heart, inasmuch as its general result is to drive 
the blood the way that the heart propels it. 

131. Effect of Expiration on the Circulation. — In expira- 
tion, the difference between the pressure of the atmosphere on 
the surface, and that which it exerts on the contents of the 
thorax through the lungs, becomes less and less in propor- 
tion to the completeness of the expiration. Whenever, by 
the ascent of the diaphragm and the descent of the ribs, 
the cavity of the thorax is so far diminished that pressure is 
exerted on the great vessels, the veins, owing to the thinness 
of their walls, are especially affected, and a check is given to 
the flow of blood in them, which may become visible as a 
venous pulse in the great vessels of the neck. In its effect on 
the arterial trunks, expiration, like inspiration, is, on the 



EFFECTS OF KESPUKATION. 108 

whole, favorable to the circulation ; the increased resistance to 
the opening of the valves during the ventricular systole being 
more than balanced by the advantage gained in the addition 
of the expiratory pressure to the elastic reaction of the arterial 
walls during the diastole. 

"When the skull of a living animal is laid open and the 
brain exposed, the cerebral substance is seen to rise and fall 
synchronously with the respiratory movements ; the rise cor- 
responding with expiration. 

132. Stoppage of the Heart by Distension of the Lungs.— 
Hitherto, I have supposed the air-passages to be freely open 
during the inspiratory and expiratory movements. But if, the 
lungs being distended, the mouth and nose are closed, and a 
strong expiratory eilbrt is then made, the heart's action may 
be stopped altogether.^ And the same result occurs if, the 
the lungs being partially emptied, and the nose and mouth 
closed, a strong inspiratory effort is made. In the latter case 
the excessive distension of the right side of the heart, in con- 
sequence of the flow of blood into it, may be the cause of the 
arrest of the heart's action, but, in the former, the reason of 
the stoppage is not very clear. 

133. Circumstances modifying Respiration. — The activ- 
ity of the respiratory process is greatly modified by the cir- 
cumstances in which the body is placed. Thus, cold greatly 
increases the quantity of air which is breathed, the quantity 
of oxygen absorbed, and of carbonic acid expelled : exercise 
and the taking of food have a corresponding effect. 

In proportion to the weight of the body, the activity of the 
respiratory process is far greatest in children, and diminishes 
gradually with age. 

The excretion of carbonic acid is greatest during the day 
and gradually sinks at night, attaining its minimum about mid- 
night, or a little after. 

The quantity of oxygen which disappears in proportion to 
the carbonic acid given out, is greatest in carnivorous, least in 

* There is dacsrer in nt tempting this experiment. 



104 ELEMENTARY PHYSIOLOGY. 

herbivorous animals — ^p^reater in a man livino: on a flesli diet, 
than when the same man is feeding on vegetable matters. 

134. Asphyxia. — When a man is strangled, drowned, or 
choked, or is, in any other way, prevented from inspiring or 
expiring sufficiently pure atmospheric air, what is called as- 
phyxia comes on. He grows " black in the face ; " the veins 
become turgid ; insensibility, not unfrequently accompanied 
by convulsive movement, sets in, and he is dead in a few 
minutes. 

But in this asphyxiating process two deadly influences of a 
distinct nature are cooperating ; one is the deprivation of oxy- 
gen^ the other is the excessive acczimulation of cay^bonic acid 
in the blood. Oxygen starvation and carbonic acid poisoning, 
each of which may be fatal in itself, are at work together. 

The effects of oxygen starvation may be studied separately 
by placing a small animal under the receiver of an air-pump 
and exhausting the air. In this case no accumulation of car- 
bonic acid is peniiitted, but, on the other hand, the supply of 
oxygen soon becomes insufficient, and the animal quickly dies. 
And if the experiment be made in another way, by placing a 
small mammal, or bird, in air from which the carbonic acid is 
removed as soon as it is formed, the animal will nevertheless 
die as soon as the amount of oxygen is reduced to ten per cent, 
or thereabouts. 

The directly poisonous effect of carbonic acid, on the other 
hand, has been very much exaggerated. A very large quantity 
of carbonic acid, ten to fifteen or twenty per cent., may be con- 
tained in air, without producing any very serious, immediate 
effect, if the quantity of ox3^gen be simultaneously increased. 

135. How it destroys Life. — ^Whichever may be the more 
potent agency, the effect of the two, as combined in asphyxia, 
is to produce an obstruction, firstly, in the pulmonary circula- 
tion, and, secondly, in the veins of the body generally. The 
lungs and the right side of the heart, consequently, become 
gorged with blood, while the arteries and left side of the heart 
gradually empty themselves of the small supply of dark and 



EFFECTS OF RESPIRATION. 105 

unaerated blood which they receive. The heart becomes par- 
alyzed, partly by reason of the distension of its right side, 
partly from being supplied with venous blood ; and all the 
organs of the body cease to act. 

136. Respiratory Poisons. — Whatever may be the case 
for carbonic acid (which seems to be a poison rather neg- 
atively, in virtue of its interference with oxygen, than from any 
positive ill qualities of its own), carbonic oxide, arseniuretted 
hydrogen, and sulphuretted hydrogen, are undoubtedly in 
themselves poisons of a deadly kind, and, when taken into the 
blood by the lungs, produce the worst effects. 

137, Slow Asphyxiation. — It is not necessary, however, 
absolutely to strangle or drown a man in order to asphyxiate 
him. As, other things being alike, the rapidity of diffusion 
between two gaseous mixtures depends on the difference of 
the proportions in which their constituents are mixed, it fol- 
lows that the more nearly the composition of the tidal air ap- 
proaches that of the stationary air, the slower will be the dif« 
fusion of carbonic acid outward and of oxygen inward, and the 
more charged with carbonic acid and defective in oxygen will 
the air in the air-cells become. And, on increasing the pro- 
portion of carbonic acid in the tidal air, a point will at length 
be reached when the change effected in the stationary air is 
too slight to enable it to relieve the pulmonary blood of its 
carbonic acid, and to supply it with oxygen to the extent 
required for its arterialization. 

In this case the blood, which passes into the left side of 
the heart, and is thence distributed to the body, being venous, 
all the symptoms of insensibility, loss of muscular power, etc., 
which have been enumerated above as the result of supplying 
the brain and muscles with venous blood, will follow, and a 
state of suffocation, or asphyxia, will supervene. 

Asphyxia takes place whenever the proportion of carbonic 
acid in tidal air reaches ten per cent, (the oxygen being dimin- 
ished in like proportion) ; and it of course makes no difference 
whether the quantity of cai'bonic acid in the air breathed is 
5* 



106 ELEMENTARY PHYSIOLOGY. 

increased by shutting out frcsli air; or by increasing the uum- 
ber of persons who are consuming the same air; or by suffer- 
ing combustion, in any shape, to carry off oxygen from the air. 

138. Vital Necessity of Ventilation, — The deprivation of 
oxygen, and the accumulation of carbonic acid, cause injury, 
however, long before the asphyxiating point is reached. Un- 
easiness and headache arise when less than one per cent, of 
the oxygen of the air is replaced by other matters ; while the 
persistent breathing of such air tends to lower the tone of the 
system, and predisposes it to disease. 

Hence the necessity of sufficient air and of ventilation for 
every human being. To be supplied with respiratory air in a 
fair state of purity, every man ought to have at least 800 cubic 
feet of space to himself, and that space ought to be freely ac- 
cessible by direct, or indirect, channels to the atmosphere. 



CHAPTER VI. 

THE SOURCES OF LOSS AND OF GAIN TO THE BLOOD. 

Section I. — Sources of Loss to the Blood. 

139. Distribution of Arterial Blood. — The blood, which 
has been aerated, or aiierialized, in the lungs by the process 
described in the preceding chapter, and then, having been car- 
ried from the lungs by the pulmonary vein to the left auricle, 
has been forced by the auricle into the ventricle and by the 
ventricle into the aorta, is distributed by the great arteries 
which spring from that vessel, as it traverses the thorax, to the 
head, the arms, and the walls of the body. Passing through 
the diaphragm (Fig. 38), the aortic trunk enters the cavity of 
the abdomen, and becomes what is called the abdominal aorta^ 
from which vessels are given off to the viscera of the abdomen. 
Finally, the main stream of blood flows into the iliac arteries, 
whence the viscera of the pelvis and the legs are supplied. 



SOURCES OF LOSS TO THE BLOOD. 107 

From the arteries the blood, as we have seen, enters the capil- 
laries and, as it traverses them, the products of the waste of 
the tissues constantly pour into it. Furthermore, as the blood 
contains living corpuscles, which, like all other living things, 
decay and die, it follows that if the blood is to be kept pure, 
the waste matters thus incessantly poured into, or generated 
in it, must be as constantly got rid of, or excreted. 

140. The Various Drains upon the Blood. — Three dis- 
tinct sets of organs are especially charged with this office of 
continually excreting carbonic acid, water, and urea. They are 
the Lungs^ the Kidneys^ and the Skin ; and hence, these three 
great organs may be regarded as keeping up so many drains 
upon the blood — as so many channels by which it is constantly 
losing substance. 

Further, the blood, as it traverses the capillaries, is con- 
stantly losing matter by exudation into the surrounding tis- 
sues. 

Another kind of loss takes place from the surface of the 
body generally, and from the interior of the air-passages and 
lungs. From the former, heat is constantly being given off by 
radiation, evaporation, and conduction ; from the latter, chiefly 
by evaporation. 

141. Loss by the Liver and Lungs. — The blood which 
enters the liver is constantly losing material to that organ ; but 
the loss is only temporary, as almost all the matter lost, con- 
verted into sugar and into bile, reenters the current of the cir- 
culation in the liver itself, or elsewhere. 

Again, the loss of matter and of heat by the lungs, in 
respiration, is partially made up by the no less constant gain 
which results from the quantity of oxygen absorbed at each 
inspiration, and from the heat generated by this oxygen in the 
tissues. And the loss by exudation from the capillaries is, in 
some degree, compensated by the gain from the lymphatics 
and ductless glands. 

142. Other Losses and Gains. — In the instances just men- 
tioned the loss and gain are constant, and go on while life and 



108 ELEMENTARY PHYSIOLOGY. 

health last. But there are certain other operations which 
cause either loss or gain to the blood, and which are not con- 
tinuous, but take place at intervals. These are, on the side of 
loss, the actions of the many secretory glands which separate 
certain substances from the blood at recurrent periods, in the 
intervals of which they are quiescent. 

On the side of gain, they are, the contractions of the 
muscles, which, during their activity, cause a great quantity of 
waste materials to appear in the blood ; and the operations of 
the alimentary canal^ which, for a certain period after it is sup- 
plied with food, pours new materials into the blood. 

Under some circumstances, the skin may become a source 
of gain by absorbing fluids. 

The sources of loss and gain to the blood may be conve- 
niently arranged in the following tabular form : 

A, Incessantly active Sources of Loss or Gain to the 

Blood. 
a. Sources of Loss. 
L Loss of matter. 

1. The lungs. 

2. The kidneys. 

3. The skin. " 

4. The liver. 

5. The tissues generally. 

IL Loss of heat, 

1. The free surfaces of the body. 

1), Sources of Gain. . 
L Gain of matter, 

1. The lungs. 

2. The liver. 

3. The spleen, ductless glands, andlymphatic system, 

4. The tissues generally. 

IL Gain of heat, 
1. The blood itself and the tissues generally. 



SOURCES OF LOSS TO THE BLOOD. 109 

B. Intermittently active Sources of Loss or Gain to 
THE Blood. 

a. Source of Loss. 

1. Many secretmg glands. 

6. Sources of Gain. 

1. The muscles. 

2. The alimentary canal. 

3. The skin. 

143. Constant Loss by the Kidneys. — In the preceding 
chapter I have described the operation by which the lungs 
withdraw from the blood much carbonic acid and water, with 
a fractional quantity of urea, and take oxygen into the blood ; 
I now proceed to the second source of continual loss, the Kid- 
neys. 

Of these organs there are two, placed at the back of the 
abdominal cavity, one on each side of the lumbar region of 
the spine. Each is shaped like the kidney of a sheep, but 
somewhat larger, — its depressed or concave side turned inward, 
and its convex side outward (Fig. 41). From the middle of 
the concave side (called the hilus) of each kidney, a long tube 
with a small bore, the Ureter^ proceeds to the bladder [BL). 
The latter is an oval bag placed in the pelvis, the walls of 
which contain abundant unstriped muscular fibre, while it is 
lined, internally, by mucous membrane, and coated externally 
by the peritoneum. The ureters open side by side, but at 
some little distance from one another, on the posterior and in- 
ferior wall of the bladder; in front of them is a single aperture 
which leads into the canal called the Urethra^ by which the 
cavity of the bladder is placed in communication with the ex- 
terior of the body. The openings of the ureters enter the 
wall of the bladder obliquely, so that it is much more easy for 
fluid to pass from the ureters into the bladder than for it to get 
the other way, from the bladder into the ureters. 

Mechanically speaking, there is Httle obstacle to the free 



110 ELEMENTARY PHYSIOLOGY. 

flow of fluid from the ureters into the bladder, and from the 
bladder into the urethra, and so outward ; but certain mus- 
cular fibres arranged circularly around the part called the 
" neck " of the bladder, which passes into the urethra, consti- 
tute what is termed a sphincter^ and are usually, during life, in 
a state of contraction, while the other muscular fibres of the 
bladder are relaxed. It is only at intervals that this state of 



"mi 




Fig. 41. 

The kidneys {K) ; ureters ( Ur) ; with the aorta {Ao\ and vena cava inferior {V.C.I.) \ 
and the renal arteries and veins. Bl. is the bladder, the top of which is cut oflf so 
as to show the openings of the ureters (1 1), and that of the urethra (2). 

matters is reversed ; and the walls of the bladder contracting, 
while the sphincter relaxes, its contents, the urine^ are dis- 
charged. But, though the expulsion of the secretion of the 
kidneys from the body is thus intermittent, the excretion itself 
is constant, and the urinary fluid incessantly flows, drop by 
drop, from the opening of the ureters into the bladder, where 
it accumulates, until its quantity is sufiicient to give rise to the 
uneasy sensations which compel its expulsion. 

144. Kidneys and Lungs compared. — The excretion of 
nitrogenous waste and water with a little carbonic acid, by the 



SOUKCES OF LOSS TO THE BLOOD. Ill 

kidneys, is tlius strictly comparable to that of carbonic acid 
water, with a little urea, by the lungs, in the air-cells of which 
carbonic acid and watery vapors are incessantly accumulating, 
to be periodically expelled by the act of expiration. But the 
operation of the renal apparatus differs from that of the respi- 
ratory organs, in the far longer intervals between the excretory 
acts, and still more in the circumstance that, while what the 
lungs take into the body is as important as what they give out, 
the kidneys take in nothing. 

145. Composition of Renal Excretions. — The renal ex- 
cretion has naturally an acid reaction, and consists of iirea 
and uric acid ; sundry other animal products of less impor- 
tance ; with saUne and gaseous matters, held in solution by a 
large quantity of water. 

The quantity and composition of the urine vary greatly ac- 
cording to the time of day, the temperature and moisture of 
the air, the fasting or replete condition of the alimentary canal, 
and the nature of the food. 

Urea and uric acid are both composed of the elements car- 
bon, hydrogen, oxygen, and nitrogen, but urea is by far the more 
soluble compound, and greatly exceeds the uric acid in quantity. 

An average healthy man excretes by the kidneys about fifty 
ounces, or 24,000 grains, of water a day. In this are dissolved 
500 grains of urea, but not more than 10 to 12 grains of uric 
acid. 

The amount of other animal matters and of saline sub- 
stances, varies from one-third as much to nearly the same 
amount as the urea. The saline matters consist chiefly of 
common salt, phosphates and sulphates of potash, soda, lime, 
and magnesia. The gases are the same as those in the blood, 
namely, carbonic acid, oxygen, and nitrogen. But the quan- 
tity is, proportionably, less than one-third as great ; and the 
carbonic acid is in very large, while the oxygen is in very small, 
amount. 

The average specific gravity does not differ very widely 
from that of blood serum, being 1-020. 



112 ELEMENTARY PHYSIOLOGY. 

146. The structure of the Kidney. — It will be observed 
that all the chief constituents of the urine are already contained 
in the blood, and indeed, it might almost be said to be the 
blood devoid of its corpuscles, fibrin, albumen, and iron. Speak- 
ing broadly, it is such a fluid as might be separated from the 
blood by the help of any kind of filter which had the property 
of retaining these constituents, and letting the rest flow ofi^. 
The filter required is found in the kidney, to the structure of 
which we must now turn. 

When a longitudinal section of a kidney is made (Fig. 42), 
the upper end of the ureter (d) seems to widen out into a basin- 
like cavity (c), which is called the pelvis of the kidney. Into 
this, sundry conical elevations project, the summits of which 
present multitudes of minute openings — the final terminations 
of the tubulin of which the thickne^r-s of the kidney is chiefly 
made up. If the tubules are traced from their openings toward 
the outer surface, they are found, at first, to lie parallel with one 




Fig. 42. 



Longitudinal section of the human kidney, a, the cortical substance ; 5, the medul- 
lary substance; c, the pelvis of the kidney ; a, the ureter. 

another in bimdles, which radiate toward that surface, and sub- 
divide as they go ; but at length they spread about irregularly, 
and become interlaced. From this circumstance alone, the 
middle, or medullary, part (marrow, medulla) of the kidney 
looks different from the superficial, or cortical, part (bark, 
cortex) ; but, in addition, the cortical part is more abundantly 



SOURCES OF LOSS TO THE BLOOD. 



113 



supplied with vessels than the medullary, and hence has a 
darker aspect. Each tubule (or, at any rate, most of them) 
ends at last in a dilatation (Fig. 43), which is called a Malpi- 
ghian capsule. Into the summit of this a small vessel (/), one 
of the ultimate branches of the renal artery^ enters, and imme- 
diately breaks up into a bunch of looped capillaries, called a 
glomerulus {h), which nearly fills the cavity of the capsule. 
The blood is carried away from this glomerulus by a small vein 
(g), which does not, at once, join with other veins into a larger 
venous trunk, but opens into the network of capillaries which 
surrounds the tubule, thus repeating the portal circulation on a 
small scale. 




Fig. 44. 

Fig. 43.— Malpighian capsule (a), with its contained .glomerulus (h) and the bedn- 
ning of the tubule (6) into which it opens. <:•, d, epithelium in place : e, epithe- 
lium of the tubule detached; /, the artery; g, the vein; h, the glomerulus. 

Fig. 44. — The epithelium magnified. 

The tubule has an epithelial lining (d) continuous with that 
of the pelvis of the kidney, and the urinary passages generally. 
The epithelium is thick and plain enouo'h in the tubule, but it 
becomes very delicate, or even disappears, in the capsule and 
on the glomerulus. 



114 ELEMENTARY PHYSIOLOGY. 

147. The Filtering Mechanism.— It is obvious from this 
description that the surface of the glomerulus is, practically, 
free, or in direct communication with the exterior ; and further, 
that, in each vessel of the glomerulus, a thiu stream of blood 
constantly flows, only separated by the very delicate membrane 
of which the wall of the vessel is composed from the cavity of 
the tubule. The Malpighian capsule may, in fact, be regarded 
as a funnel, and the membranous walls of the glomerulus as a 
piece of very delicate filtering paper, into which the blood is 
poured. 

148. Changes of the Blood while passing through the 
Kidneys. — The blood whicli supplies the kidneys is brought 
directly from the aorta by the renal arteries, so that it has but 
shortly left the heart. The venous blood which enters the 
heart and is propelled to the lungs, charged vrith the nitro- 
genous, as well as with the other, products of waste, loses only 
an inappreciable quantity of them in its course through the 
lungs ; so that the arterial blood which fills the aorta is pure 
only as regards carbonaceous waste, impure as regards urea and 
uric acid. 

In the healthy condition, the w^alls of the minute renal 
arteries and veins are relaxed, so that the passage of the blood 
is very free, and but little waste, arising from muscular con- 
traction, is thrown into the renal blood. Furthermore, as the 
urine contains very little oxygen and much carbonic acid, such 
carbonaceous waste as arises from this source is probably 
counterbalanced. Hence, so long as the kidney is performing 
its functions properly, the blood which leaves the organ by the 
renal vein is as bright scarlet as that which enters it by the 
renal artery. Strictly speaking, it is the purest blood in the 
body, careful analysis having shown that it contains a sensibly 
smaller quantity of urea and of water than that of the left side 
of the heart. 

This diflerence is, of course, a necessary result of the excre- 
tion of the urinary fluid from the blood as it travels through 
the kidney ; what is less intelligible, at present, is the circum- 



SOURCES OF LOSS TO THE BLOOD. 115 

stance that the plasma of the blood of the renal vein yields 
little or no fibrin, and hence differs but little from serum. 

149. The Hervous System controls the Renal Excretion. 
— Irritation of the nerves which supply the walls of the vessels 
of the kidney has the immediate effect of stopping the excre- 
tion of urine, and rendering the renal blood dark and venous. 
The first effect would appear to be explicable by the diminu- 
tion of the pressure exerted upon the blood in the Malpighian 
tufts, in consequence of the diminution in size of the channels 
— the small arteries — ^by which the blood reaches them. And 
the second effect is probably, in part, a consequence of the 
first — the excretion of carbonic acid by the urine ceasing; 
while, to a greater extent, it is the result of the pouring in of 
carbonic acid into the renal blood, in consequence of the work 
of the muscles of the small vessels, and the waste which results 
therefrom. 

150. The Loss by the Skin.— That the sJcin is a source of 
continual loss to the blood may be proved in various ways. If 
the whole body of a man, or one of his limbs, be enclosed in a 
caoutchouc bag, full of air, it will be found that this air under- 
goes changes which are similar in kind to those which take 
place in the air which is inspired into the lungs. That is to 
say, the air loses oxygen and gains carbonic acid; it receives 
a great quantity of watery vapor, which condenses upon the 
sides of the bag, and may be drawn off by a properly disposed 
pipe ; and, furthermore, a minute quantity of urea accumulates 
upon the surface of the limb or body. Under ordinary cir- 
cumstances no liquid water appears upon the surface of the 
integument, and the whole process receives the name of the in- 
sensible perspiration. But, when violent exercise is taken, or 
under some kinds of mental emotion, or when the body is 
exposed to a hot and moist atmosphere, the perspiration be- 
comes sensible^ — is visible in the form of scattered drops upon 
the surface. 

151. Quantity of the Cutaneous Excretions. — The quan- 
tity of sweat, or perspiration, varies immensely, according to 



116 ELEMENTARY PHYSIOLOGY. 

the temperature and other conditions of the air, and according 
to the state of the blood and of the nervous system. It is 
estimated that, as a general rule, the quantity of water ex- 
creted by the skin is about double that given out by the lungs 
in the same time. The quantity of carbonic acid is not above 
-gig-th or ^th that excreted by the lungs. The precise quantity 
of urea excreted is not known. 

In its normal state the sweat is acid, and contains fatty 
matters, even when obtained free from the fatty products of 
the sebaceous glands. Ordinarily, perspiration, as it collects 
upon the skin, is mixed with the fatty secretion of these 
glands ; and, in addition, contains scales of the external layers 
of the epidermis, which are constantly being shed. 

152. Pespiration by Simple Transudation. — In analyzing 
the process by which the perspiration is eliminated from the 
body, it must be recollected, in the first place, that the skin, 
even if there were no glandular structures connected with it, 
would be in the position of a moderately thick, permeable 
membrane, interposed between a hot fluid, the blood, and an 
atmosphere which is, usually, far from saturated with watery 
vapor, and which, at any rate in temperate climates, ceases to 
be so saturated the moment it comes into contact with the 
skin, the temperature of which is, ordinarily, twenty or thirty 
degrees above its own. 

A bladder filled with water at 100°, though it possess no 
sensible pores, will assuredly allow evaporation to take place 
freely through its substance ; and, from its relation to the blood, 
the skin is such a bladder full of hot fluid. 

Thus, perspiration to a certain amount must always be 
going on through the substance of the integument ; but what 
the amount of this perspiration may be, cannot be ascertained, 
because a second and very important source of the perspira- 
tion is to be found in what are called the sweat-glands, 

153. Sweat-glands. — All over the body the integument 
presents minute apertures, the ends of channels excavated in 
the epidermis or scarf-skin, and each continuing the direction 



SOURCES OF LOSS TO THE BLOOD. 



117 



of a minute tube, usually about -^-Jo^^ ^^ ^^ ^^^^ ^^ diameter, 
and a quarter of an inch long, which is imbedded in the dermis. 
Each tube is lined with an epitheUum continuous with the epi- 
dermis. The tube sometimes divides, but, whether single or 
branched, its inner end or ends are blind, and coiled up into a 
sort of knot, interlaced with a meshwork of capillaries (Fig. 45). 
The blood in these capillaries is therefore separated from the 
cavity of the sweat-gland only by the thin walls of the capil- 
laries, that of the glandular tube, and its epithelium, which, 
taken together, constitute but a very thin pellicle ; and the ar- 
rangement, though different in detail, is similar in principle, 
to that which obtains in the kidney. In the latter, the vessel 




Fig. 46. 



Fig. 45. 

Fig. 45.— Section of the skin showing the sweat-dands. a, the epidermis ; h^ its deep- 
er layer, the rete Malpiqliii ; e d, the dermis, or true skin ; f, fat cells ; j?, the 
coiled end of a sweat-gland ; /i, its duct ; «, its opening on the surface of the 
epidermis. 

Fig. 46.— A section of the skin showing the roots of the hairs and the sebaceous 
glands ; b, muscle of ; c, the hair-sheath on the left hand. 

makes a coil within the Malpighian capsule, wdiich ends a 
tubule. Here the perspiratory tubule coils about, and among, 
the vessels. In both cases the same resnlt is arrived at — 
namely, the exposure of the blood to a large, relatively free, 
surface, on to which certain of its contents transude. 

The number of these glands varies in different parts of the 



118 ELEMENTARY PHYSIOLOGY. 

body. They are fewest in the back and neck, where their 
number is not much more than 400 to a square inch. They 
are more numerous on the skin of the palm and sole, where 
their apertures follow the ridges visible on the skin, and amount 
to between two and three thousand on the square inch. At a 
rough estimate, the whole integument probably possesses not 
fewer than from two millions and a quarter to two milHons and 
a half of these tubules, which therefore must possess a very great 
aggregate secreting power. 

154. These Glands are controlled by the Nervous System. 
— The sweat-glands arc greatly under the influence of the 
nervous system. This is proved, not merely by the well- 
known effects of mental emotion in sometimes suppressing the 
perspiration and sometimes causing it to be poured forth in 
immense abundance, but has been made a matter of direct ex- 
periment. There are some animals, such as the horse, which 
perspire very freely. If the sympathetic nerve of one side, in 
the neck of a horse, be cut, the temperature of that side of the 
head rises, and it becomes injected with blood (par. 74) ; and, 
at the same time, sweat is poured out abundantly over the 
whole surface thus affected. On irritating the end of the cut 
nerve, which is in connection with the vessels, the muscular 
walls of the latter, to which the nerve is distributed, contract, 
the congestion cea.ses, and with it the perspiration. 

155. Variations in the Perspiratory Losses. — The quan- 
tity of matter which may be lost by perspiration, under certain 
circumstances, is very remarkable. Heat and severe labor 
combined, may reduce the weight of a man two or three 
pounds in an hour, by means of the cutaneous perspiration 
alone ; and, as there is some reason to believe, that the quantity 
of solid matter carried off from the blood does not diminish 
with the increase of the amount of the perspiration, the quan- 
tity of urea eliminated by profuse sweating may be consider- 
able. 

The difference between blood which is coming from, and 
that which is going to, the skin, can only be concluded from 



SOURCES OF LOSS TO THE BLOOD. 119 

the nature of the substances given out m the perspiration; but 
arterial blood is not rendered venous in the skin. 

156. The Lungs, Skin, and Kidneys compared. — It will 
now be instructive to compare together, in more detail than has 
been done in the second chapter, the three great organs — lungs, 
kidneys, and skin — which have been described. 

In ultimate anatomical analysis, each of these organs con- 
sists of a moist animal membrane separating the blood from 
the atmosphere. 

Water, carbonic acid, and urea pass out from the blood 
through the animal membrane in each organ, and constitute 
its secretion or excretion ; but the three organs diflfer in the 
absolute and relative amounts of the constituents of which they 
permit the escape. 

Taken by weight, w^ater is the predominant excretion in 
all three : most solid matter is given off by the kidneys ; most 
gaseous matter by the lungs. 

The skin partakes of the nature of both lungs and kidneys, 
seeing that it absorbs oxygen and exhales carbonic acid and 
water, like the former, while it excretes urea and saline matter 
in solution like the latter; but the skin is more closely related 
to the kidneys than to the lungs. Hence, when the free action 
of either of the two former organs is interrupted, its work is 
usually throAvn upon the other. In hot w^eather, when the ex- 
cretion by the skin increases, that of the kidneys diminishes, 
and the reverse is observed in cold weather. 

This power of mutual substitution, however, only goes a 
little way ; for if the kidneys be extirpated, or their functions 
much interfered with, death ensues, however active the skin 
may be. And, on the other hand, if the skin be covered with 
an impenetrable varnish, the temperature of the body rapidly 
falls, and death takes place, though the lungs and kidneys re- 
main active. 



120 



ELEMENTARY PHYSIOLOGY. 



Section II. — Losses and Gains hy the Liver. 

157. Structure and Connectioiis of the Liver. — The liver 
is a constant source both of loss, and, in a sense, of gain to the 
blood : of lossy because it forms from the blood a peculiar fluid, 
the hile ; of gain, if not in quantity, at any rate in kind of mat- 
ter, because it elaborates from the blood which enters it, a sub- 
stance, glycogen^ which is capable of passing very readily into 
a kind of sugar, called glucose. Furthermore, it is very prob- 
able that the liver is one source of the colorless corpuscles of 
the blood. 

The liver is the largest glandular organ in the body, ordi- 
narily weighing about fifty or sixty ounces. It is a broad, 
dark, red- colored organ, which lies on the right side of the 
body, immediately below the diaphragm, with which its upper 
surface is in contact, while its lower surface touches the intes-^ 
tines and the right kidney. 

The liver is invested by a coat of peritoneum, which keeps 
it in place. It is flattened from above downward, convex and 




The liver viewed from below. 



Fig. 47. 

a, vena cava ; h, vena portae ; e, bile duct ; <?, hepatic 
artery ; I, gall-bladder. 



smooth above, where it fits into the concavity of the lower sur- 
face of the diaphragm. Flat and irregular below (Fig. 47), 
it is thick behind, but ends in a thin edge in front. 



LOSSES AND GAINS EY THE LIVER. 121 

Viewed from below, as in Fig. 47, tlie inferior vena cava, 
a, is seen to traverse a notch in the hinder edge of the liver as 
it passes from the abdomen to the thorax. At b the trunk of 
the vena portce is observed dividing into the chief branches 
which enter into, and ramify through, the substance of the 
organ. At d, the hepatic artery, coming almost directly from 
the aorta, similarly divides, enters the liver, and ramifies through 
it ; while at c is the single trunk of the duct, called the 
hepatic duct, which conveys away the bile brought to it by its 




Fig. 48. 
a, ultimate branclies of the hepatic duct; &, liver-cells. 

right and left branches from the liver. Opening into the he- 
patic duct is seen the duct of a large oval sac, /, the gall-hlad- 
der. The duct is smaller than the artery, and the artery than 
the portal vein. 

If the branches of the artery, the portal vein, and the bile 
duct, be traced into the substance of the liver, they will be 
found to accompany one another, and to branch out and sub- 
divide, becoming smaller and smaller. At length the portal 
vein and hepatic artery will be found to end in the capillaries, 
which traverse, like a net-work, the substance of the smallest 
obvious subdivisions of the liver substance — polygonal ma-ses 
of one-tenth of an inch in diameter, or less, which are tormod 
the lobules. Every lobule is seated by its base upon one oi the 
ramifications of a great vein — the hepatic vein — and the blood 
6 



122 



ELEMENTAEY PHYSIOLOGY. 



of its capillaries is poured into that vein by a minute veinlet 
which traverses the centre of the acinus, and pierces its base. 
Thus the venous blood of the portal vein and the arterial blood 



jrK\ 




Fig. 49. 

A section of part of the liver, to show H. V. the hepatic vein, with L. the lobules or 
acini of the liver, seated upon its walls, and sending their intralobular veins 
into it. 



of the hepatic artery reach the surface of the lobules by the 
ultimate ramifications of that vein and artery, become mixed in 
the capillaries of the acinus, and are carried off by its intra- 
lobular veinlet, which pours its contents into one of the rami- 
fications of the hepatic vein. These ramifications, joining 
together, form larger and larger trunks, which at length reach 
the hinder margin of the liver, and finally open into the vena 
cava inferior, where it passes upward in contact w^ith that part 
of the organ. 

Thus the blood with which the liver is supplied is a mixture 
of arterial and venous blood. 



LOSSES AND GAINS BY THE LIVER. 123 

What ultimately becomes of the ramifications of the hepatic 
duct is not certainly known. Lined by an epithelium, which 
is continuous with that of the main duct, and thence with that 
of the intestines, into which the main duct opens, they may be 
traced to the very surface of the lobules, but no farther. 
Whether they end blindly, as some think, or whether, as others 
conceive, they expand and close the liver-cells, is not clearly 
proved. In either case, any fluid separated from the blood by 
the lobules, must readily find its way into them. 

In the lobules themselves all the meshes of the blood-ves- 
sels are occupied by the liver-cells, many-sided minute bodies, 
each about ^oVo"^^ ^^ ^^ ^"^^ ^^ diameter, possessing a nucleus 
in its interior, and frequently having larger and smaller granules 
of fatty matter distributed through its substance (Fig. 48, b). 
It is in these that the active powers of the liver arc supposed 
to reside. 

158. The Active Powers of the Liver-Cells. — The nature 
of these active powers is determined by ascertaining — 

a. The character of that fluid, the bile, which incessantly 
flows down the biliary duct, and which, if digestion is not going 
on, and the passao-e into the intestine is closed, flows back into 
and fills the gall-bladder. 

And h. The difference between the blood which enters the 
liver and that which leaves it in respect of the constituents of 
the bile. 

159. The Bile— its duantity and Composition. — a. The 
total quantity of bile secreted in the twenty-four hours varies, 
but probably amounts to not less than from two to three 
pounds. It is a greenish-yellow, slightly alkaline, fluid, of ex- 
tremely bitter taste, consisting of water, with fi'om 17 per cent, 
of solid matter, to half that quantity, in solution. The solids 
consist chiefly of a resinous substance, composed of carbon, 
hydrogen, oxygen, nitrogen, and sulphur, which exists in com- 
bination with soda. This biliary matter, or h'din, may be sepa- 
rated by chemical processes into two acids, called the Tauro- 
cholic (which contains all the sulphur) and the Ghjcocholic ; 



124 ELEMENTARY PHYSIOLOGY. 

and it is consequently said to be a combination of taurocholate 
and glycoclwlate of soda. Besides this bilin, its chief con- 
stituent, the bile contains a crystallized fatty substance, choles- 
terine, together with a peculiar coloring matter which contains 
iron, and is probably related to the hsematin of the blood. 

h. Of these constituents of the bile the water, the choles- 
terine, and the saline matters, alone, are discoverable in the 
blood; and though doubtless some difference obtains between 
the blood which enters the liver and that which leaves it, in 
respect of the proportional quantity of these constituents, 
great practical difficulties lie in the w^ay of the precise ascer- 
tainment of those differences. The blood of the hepatic vein, 
however, is certainly poorer in water than that of the portal vein. 

160. Bile is formed in the Liver-Cells. — As the essential 
constituent of bile, hilin, is not discoverable in the blood 
which enters the liver, it must be formed at the expense of 
the tissue of that organ itself, or of some constituent of the 
blood passing through it. However this may be, it is a very 
curious circumstance that, as almost all the bile which is 
formed in the intestines is reabsorbed by the vessels in their 
walls, it must, in some shape or other, enter the liver a second 
time with the current of the portal blood. 

Section HI. — Sources of Gain to the Blood. 

161. The Skin as an Organ of Respiration. — We must 

next consider the chief sources of constant gain to the blood ; 
and, in the first place, the sources of gain of matter. 

The lungs and skin are, as has been seen, two of the prin- 
cipal channels by which the body loses liquid and gaseous 
matter, but they are also the sole means by which one of the 
most important of all substances for the maintenance of life, 
oxygen, is introduced into the blood. It has already been 
pointed out that the volume of the oxygen taken into the blood 
by the lungs is rather greater than that of the carbonic acid 
given out. 



SOURCES OF GAIN TO THE BLOOD. 125 

How much is taken in by the skin of man is not certainly 
known, but in some of the lower animals, such as the frog, the 
skin plays a very important part in the performance of the 
respiratory function. 

162. Reaction of the Liver upon the Blood — The blood 
leaving the liver by the hepatic vein not only contains pro- 
portionally less water and fibrin, but proportionally more cor- 
puscles, especially colorless corpuscles, and, what is still more 
important, a larger quantity of liver-sugar, or glucose^ than that 
brought to it by the portal veins and hepatic artery; and 
these differences are irrespective of the nature of the food. 

That the blood leaving the liver should contain propor- 
tionally less water and more corpuscles than that entering it 
is no more than might be expected, from the fact that the for- 
mation of the bile, which is separated from this blood, neces- 
sarily involves a loss of water and of some solid matters, while 
it does not abstract any of the corpuscles. 

We do not know why less fibrin separates from the blood 
of the hepatic vein than from the blood brought to the liver. 
But the reason why there is always more sugar in the blood 
leaving the liver than in that entering it ; and why, in fact, 
there is plenty of sugar in the blood of the hepatic vein even 
when none whatever is brought to it by the hepatic artery, or 
portal vein, has only been made out by careful and ingenious 
experimental research within the last few years. 

163. Proof of the Sugar-forming Function of the Liver. — 
If an animal be fed upon purely animal food, the blood of the 
portal vein will contain no sugar, none having been absorbed 
by the walls of the alimentary canal, nor v/ill that of the he- 
patic artery contain any, or, at any rate, but the merest trace. 
Nevertheless, plenty will be found, at the same time, in the 
blood of the hepatic vein and in that of the vena cava, from 
the point at which that vein opens, as far as the heart. 

Secondly, if, from an animal so fed, the liver be extmcted, 
and a current of cold water forced into the vena portce^ it will 
flow out by the hepatic vein, carrying with it all the blood of 



126 ELEMENTARY PHYSIOLOGY. 

the organ, and will, after a time, pour out colorless, and de- 
void of sugar. Nevertheless, if the organ be left to itself at a 
moderate temperature, sugar will soon again become abundant 
in it. 

Thirdly, from the liver, washed as above described, a sub- 
stance may be extracted, by appropriate methods, which re- 
sembles starch, dextrine, and gum in chemical composition, 
consisting as it does of carbon united with hydrogen and oxy- 
gen, the latter being in the same proportions as in water. 
This '' amyloid " substance is glycogen. It may be diied and 
kept without change for long periods. 

But, like the vegetable starch and dextrine, this animal 
amyloid, which is necessarily formed in the liver, since it is 
certainly not contained either in the blood of the portal vein, 
or in that of the hepatic artery, is very readily changed by 
contact with many nitrogenous matters, which act as ferments, 
into sugar. 

Fourthly, it may be demonstrated that a nitrogenous fer- 
ment, competent to change the " amyloid " glycogen into 
saccharine ^' glucose, '^^ exists under ordinary circumstances in 
the liver. 

Putting all these circumstances together, the riddle of the 
appearance of sugar in the blood of the hepatic vein and vena 
cava, when neither it nor any compound out of which it is 
easily formed exists in the blood brought to the liver, is 
readily explained. 

The liver forms glycogen out of the blood w^ith which it 
is supplied. The same blood supplies the ferment w^hich, at 
the temperature of the body, very speedily converts that com- 
paratively little soluble glycogen into very soluble sugar; and 
this sugar is dissolved and carried away by each intralobular 
vein to the hepatic vein, and thence to the vena cava. 

164. Gain by the Lymphatics. — The lymjjhatic sijstem has 
been already mentioned as a feeder of the blood wuth a fluid 
which, in general, appears to be merely the superfluous drain- 
age, as it were, of the blood-vessels ; though at intervals, as 



SOURCES OF GAIN TO THE BLOOD. 



127 



we shall see, the lacteals make substantial additions of new 
matter. It is very probable that the multitudinous lymphatic 
glands may effect some change in the fluid which traverses 
them, or may add to the number of corpuscles in the lymph. 

The glandular bodies, which like the lymphatic glands are 
devoid of ducts and are abundantly supplied with lymphatics, 
are the thyroid gland, which lies in the part of the throat below 
the larynx, and is that organ which when enlarged by disease 
gives rise to " Derbyshire neck " or " goitre ; " the thymus 
gland, situated at the base of the heart, largest in infants, and 
gradually disappearing in adult and old persons ; and the supra 
o-enal capsules, which lie above the kidneys. Nothing is cer- 
tainly known of the functions of any of these bodies. 

165. The Spleen— its Functions unknown. — We are as 
much in the dark respecting the office of the large viscus 



Z>7n. 




Fig. 50. 

The spleen (Spl.) with the splenic artery {Sp. AX Below this is seen the splenic vein 
ninnins: to help to form the vena porta' {V.P.). Ao. the aorta: I), a pilhir of 
tlic diaphratrm ; P. D. the pancreatic duct exposed by Gissecticn in the sub- 
stance ol the pancreas ; D. M. the duodenum ; B. D. the biliary duct opening 
with the pancreatic duct at x ; ?/, the intestinal vessels. 

called the spleen, which lies upon the left side of the stomach 
in the abdominal cavity. It is an elongated flattened red 
body, abundantly supplied with blood by an artery called the 



128 ELEMENT AKY PHYSIOLOGY. 

splenic artery^ Avliicli proceeds almost directly from the aorta. 
The blood which has traversed the spleen is collected by the 
S2Jlenic vein, and is carried by it to the vena portce, and so to 
the liver. 

A section of the spleen shows a dark red spongy mass 
dotted over with minnte wdiitish spots. Each of these last is 
the section of one of the spheroidal bodies called co7yuscles of 
the spleen, which are scattered through its substance, and con- 
sist of a solid aggregation of bodies, like the white corpuscles 
of the blood, traversed by a capillary net-work, which is fed by 
a small twig of the splenic artery. The dark-red part of the 
spleen in which these corpuscles are imbedded is composed of 
fibrous and elastic tissue supporting a very spongy vascular 
net-work. 

The elasticity of the splenic tissue allows the organ to be 
readily distended, and enables it to return to its former size 
after distension. It appears to change its dimensions with the 
state of the abdominal viscera, attaining its largest size about 
six hours after food is taken, and falling to its minimum bulk 
six or seven hours later, if no food be taken. 

The blood of the splenic vein is found to contain propor- 
tionally fewer red corpuscles, but more colorless corpuscles and 
more fibrin, than that in the splenic artery ; and it has been sup- 
posed that the spleen is one of those parts of the economj^ in 
which the colorless corpuscles of the blood are especially pro- 
duced. 

166. The Gain of Heat— its Source. — It has been seen that 
heat is being constantly given off from the integument and 
from the air-passages : and every thing that passes from the 
body carries away wdth it, in like manner, a certain quantity 
of heat. Furthermore, the surface of the body is much more 
exposed to cold than its interior. Nevertheless, the tempera- 
ture of the body is maintained very evenly at all times and in 
all parts, within the range of two degrees on either side of 99° 
Fahrenheit. 

This is the result of three conditions: — The first, that heat 



SOURCES OF GAIN TO THE BLOOD. 129 

IS constantly being generated in the body. The second, that 
it is as constantly being distributed through the body. The 
third, that it is subject to incessant regulation. 

Heat is generated whenever oxidation takes place ; and 
hence, whenever protein substances, or fats or amyloidal mat- 
ters, are being converted into the more highly oxidated waste 
products, urea, — -uric acid, carbonic acid, and water, — heat is 
necessarily evolved. But these processes are taking place in 
all parts of the body by which vital activity is manifested, and 
hence, every capillary vessel and every extravascular islet of 
tissue is really a small fireplace in which heat is being evolved, 
in proportion to the activity of the chemical changes which 
are going on. 

167. Bistribution of Heat by the Blood-Current. — But 
as the vital activities of diff'erent parts of the body, and of the 
whole body, at different times, are very different ; and as some 
parts of the body are so situated as to lose their heat by radia- 
tion and conduction much more easily than others, the tem- 
perature of the body would be very unequal in its different 
parts and at different times, were it not for the arrangements 
by which the heat is distributed and regulated. 

Whatever oxidation occurs in any part, raises to an equiv- 
alent temperature the blood which is in that part at the time. 
But this blood is swiftly hurried away into other parts of the 
body, and rapidly parts with its increased temperature to them. 
On the other hand, the blood of the surface of the body, the 
temperature of which is lowered by evaporation and radiation, 
suffers only a very slight loss of heat before it is transported 
into the deeper parts and there becomes warmed by contact, 
as well as by the oxidating processes in which it takes a part. 
Thus the organs of circulation are comparable to a vast system 
of hot-water pipes — the constant flow of fluid through which 
should be effected by a pump, wdiile the water should bo 
warmed, not by a great central boiler as usual, but by a nud- 
titude of minute gas-jets, disposed beneath the pipes, not 
evenly, but more here and fewer there. It is obvious that. 



130 ELEMENTARY PHYSIOLOGY. 

however much greater the heat apphed to one part of the sys- 
tem of pipes than to another, the general temperature of the 
water would be even throughout, if it were kept moving with 
sufficient quickness by the pump. 

168. Evaporation regulates Temperature. — If such a 
system were entirely composed of closed pipes, the temperature 
of the water might be raised to any extent by the gas-jets. On 
the other hand, it might be kept down to any required degree 
by causing a larger, or smaller, portion of the pipes to be wet- 
ted with water, which should be able to evaporate freely — as, 
for example, by wrapping them m wet cloths. And the 
greater the quantity of water thus evaporated, the lower would 
be the temperature of the whole. 

Now the regulation of the temperature of the human body 
is effected on this principle. The vessels are closed pipes, but 
a great number of them are enclosed in the skin and in the 
mucous membrane of the air-passages, which are, in a physical 
sense, wet cloths freely exposed to the air. It is the evapora- 
tion from these which exercises a more important influence 
than any other condition upon the regulation of the tempera- 
ture of the blood, and consequently of the body. 

169. Regulative Agency of the Nervous System. — But as 
a further nicety of adjustment, the wetness of the regulator is 
itself determined by the state of the small vessels, inasmuch as 
exudation from these takes place more readily when the walls 
of the veins and arteries are relaxed, and the blood distends 
them and the capillaries. But the condition of the walls of 
the vessels depends upon the nerves by which they are sup- 
plied, and it so happens that cold produces irritation of these 
nerves with contraction of the small vessels — moderate warmth, 
the reverse. 

Thus the supply of blood to the surface is lessened and loss 
of heat thereby checked, when the external temperature is 
low ; while, when the external temperature is high, the supply 
of blood to the surface is increased, the fluid exuded from the 
vessels pours out by the sweat-glands, and the evaporation of 



S0UKCE8 OF GAIN TO THE BLOOD. 



131 



this fluid checks the rise in the temperature of the superficial 
blood. 

Hence it is that, so long as the surface of the body per- 
spires freely, and the air-passages are abundantly raoist, a man 
may remain with impunity, for a considerable time, in an oven 
in which meat is being cooked. The heat of the air is ex- 
pended in converting his superabundant perspiration into va- 
por, and the temperature of the blood is hardly raised. 

170. Intermittent Action of the Glands. — The chief inter- 
mittently active sources of loss to the blood are found among 
the glands proper, all of which are, in principle, narrow pouches 
of the mucous membranes, or of the integument of the body, 
lined by a continuation of the epithelium or of the epidermis. 
In the glands of LieherkuhUj which exist in immense numbers 
in the walls of the intestines, each gland is nothing more than 
a simple blind sac of the mucous membrane, shaped like a 
small test-tube, with its closed end outward, and its open end 
on the inner surface of the intestine. The svveat-erlands of the 




Fig. 52. 
Fig. 51.— A salivary duct, with 5, its lateral ramifications, and cf, the ultimate blind 

ends of these. 
Fig. 52. — Two of the bliud ends magnified. 

skin, as we have already seen, are equally simple, blind, tube- 
like involutions of the integument, the ends of which become 
coiled up. The sebaceous glands, usually connected with the 



132 ELEMENTARY PHYSIOLOGY. 

hair-sacs, are shorter, and their blind ends somewhat sub- 
divided, so that the gland is divided into a narrow neck and a 
more dilated and sacculated end. The neck by which the 
gland communicates with the free surface is now called its ducL 
More complicated glands are produced by the elongation of 
the duct into a long tube, and the division and subdivision of 
the blind end into multitudes of similar tubes, each of which 
ends in a dilatation. These dilatations, attached to their 
branched ducts, somewhat resemble a bunch of grapes. Glands 
of this kind are called racemose. The salivary/ glands and the 
pancreas are such glands. 

Now, many of these glands, such as the salivary, the pai> 
creas (and the perspiratory, or sudoriparous glands, which it 
has been convenient to consider already), are only active w^hen 
certain impressions on the nervous system give rise to a par- 
ticular condition of the gland, or of its vessels, or of both. 

171. Action of the Salivary Glands. — Thus the sight or 
smell, or even the thought of food, will cause a flow of saliva 
into the mouth ; the previously quiescent gland suddenly pour- 
ing out its fluid secretion, as a result of a change in the con- 
dition of the nervous system. And, in animals, the salivary 
glands can be made to secrete abundantly, by irritating a nerve 
which supplies the gland and its vessels. How far this eflect 
is the result of the mechanical influence of the nen^e' on-the 
state of the circulation, and how far it is the result of a more 
direct influence of the nerve upon the state of the tissue of the 
gland itself, is not at present determined. 

The liquids poured out by the intermittent glands are al- 
ways very poor in solid constituents, and consist chiefly of 
water. Those poured on to the surface of the body are lost, 
but those which are received by the alimentary canal are doubt- 
less in great measure reabsorbed. 

172. Gain of Waste Products from the Muscles.— The 
great intermittent sources of gain of waste products to the blood 
are the muscles, every contraction of which is accompanied by 
a waste of matter, and a pouring of their waste products into 



PROPERTIES OF FOOD-STUFFS. 166 

the blood. That much of this waste product is carbonic acid 
is certain from the facts, (a) that the blood which leaves a con- 
tracting muscle is always highly venous, far more so than that 
which leaves a quiescent muscle ; and (b) that muscular exer- 
tion at once immensely increases the quantity of carbonic acid 
expired : but whether the amount of nitrogenous waste is in- 
creased under these circumstances, or not, is a point yet under 
discussion. 



CHAPTER VII. 

THE FUNCTION OF ALIMENTATION. 

Section I. — Properties of Food-Stuffs. 

173. The Alimentary Canal the Chief Source of Gain,— 

The great source of gain to the blood, and, except the lungs, 
the only channel by which altogether new material is intro- 
duced into that fluid, is the alimentary canal^ the totality of 
the operations of which constitute the function of alimentation. 
It will be useful to consider the general nature and results of 
the performance of the function of alimentation before study- 
ing its details. 

174. Quantity of Dry, Solid, and Gaseous Aliment daily 
taken. — A man daily takes into his mouth, and thereby intro- 
duces into his alimentary canal, a certain quantity of solid and 
liquid food, in the shape of meat, bread, butter, water, and the 
like. The quantity of chemically dry, solid matter, which 
must thus be taken into the body, if a man of average size and 
activity is neither to lose, nor to gain, in weight, has been 
found to be about 8,000 grains. In addition to this his blood 
absorbs by the lungs about 10,000 grains of oxygen gas, mak- 
ing a grand total of 18,000 grains (or nearly two pounds and 
three-quarters avoirdupois) of daily gain of dry, solid, and gas- 
eous matter. 



134 ELEMENTARY PHYSIOLOGY. 

175. Daily Loss of Dry Solids. — The weight of dry solid 
matter passed out from the alimentary canal does not, on the 
average, amount to more than one-tenth of that which is taken 
into it, or 800 grains. By no other channel does any appre- 
ciable quantity of solid matter leave the body, and it therefore 
follows that 7,200 grains of solid must pass out of it, in either 
the gaseous or the liquid form, as well as the 10,000 grains of 
oxygen. Further, as the general composition of the body re- 
mains constant, it follows, either that the elementary constitu- 
ents of the solids taken into the body must be identical with 
those of the body itself: or that, in the course of the vital pro- 
cesses, the food alone is destroyed, the substance of the body 
remaining unchanged : or, finally, that both these alternatives 
hold good, and that food is, partly, identical with the wasting 
substance of the body and replaces it; and, partly, differs 
from the wasting substance, and is consumed without repla- 
cing it. 

176. Classification of Aliments. — As a matter of fact, all 
the substances which are used as food come under one of four 
heads. They are either what may be termed Froteids, or they 
are Fats, or they are Amyloids, or they are Minerals, 

Proteids are substances analogous in composition to Protein^ 
and contain the four elements — carbon, hydrogen, ox^en, and 
nitrogen, sometimes united with sulphur and phosphorus. 

Under this head come the Gluten of flour ; the Albumen 
of white of egg, and of blood serum ; the Fibrin of the blood ; 
the Syntonin^ which is the chief constituent of muscle and 
flesh, and Casein, the chief constituent of cheese ; while Gelatin, 
which is obtained by boiling from connective tissue, and Chon- 
drin, which may be produced in the same way from cartilage, 
may be considered to be outlying members of the same group. 

Fats are composed of carbon, hydrogen, and oxygen only, 
and contain more hydrogen than is enough to form water if 
united with the oxygen which they possess. 

All oils and vegetable and animal fatty matters come under 
this division. 



PHOPEETIES OF FOOD-STUFFS. 135 

Amj/loids are substances whicli also consist of carbon, by* 
drogen, and oxygen only. But they contain no more bydro- 
gen tban is just sufficient to produce water witb tbeir oxygen. 
Tbese are tbe matters known as Starchy Dextrine, Sugar, and 
Gum, 

It is tbe peculiarity of tbe tbree groups of food-stuffs just 
mentioned tbat tbey can only be obtained (at any rate, at 
present) by tbe activity of living beings, wbetber animals or 
plants, so tbat tbey may be conveniently termed vital food-stnffs. 

Food-stuffs of tbe fourtb class, on tbe otber band, or Min- 
erals, are to be procured as well from tbe not-living, as tbe 
living, world. Tbey are water, and salts of sundry alkalies, 
eartbs, and metals. To tbese, in strictness, oxygen ougbt to be 
added, tliougb, as it is not taken in by tbe alimentary canal, it 
hardly comes witbin tbe ordinary acceptation of tbe word food. 

177. Ultimate Composition of Aliments. — In ultimate 
analysis, tben, it appears tbat vital food-stuffs contain eitber 
tbree or four of tbe elements : carbon, bydrogen, oxygen, and 
nitrogen ; tbat mineral food-stuffs are water and salts. But 
tbe buman body, in ultimate analysis, also proves to be com- 
posed of tbe same four elements, plus water, and tbe same 
saline matters as are found in food. 

More tban tbis, no substance can serve permanently for 
food — tbat is to say, can prevent loss of weigbt and cbange in 
tbe general composition of tbe body — unless it contains a cer- 
tain amount of protein in tbe sbape of albumen, fibrin, syntonin, 
or casein. While, on tbe otber hand, any substance which 
contains protein in a readily assimilable shape, is competent to 
act as a permanent food. 

But the human body, as we have seen, contains a laro^e 
quantity of protein in one or tbe other of the four forms which 
have been enumerated ; and, therefore, it turns out to be an 
indispensable condition, tbat every substance which is to serve 
permanently as food, must contain a sufficient quantity of tbe 
most important and complex component of tbe body ready 
made. It must also contain a sufficient quantity of the mineral 



136 ELEMENTARY PHYSIOLOGY. 

ingredients which are required. Whether it contains either 
fats or amyloids, or both, or is devoid of both, its essential 
power of supporting the life and maintaining the weight and 
composition of the body remains unchanged. 

178. No absolute Necessity for other Food-Stuffs. — The 
necessity of constantly renewing the supply of protein arises 
from the circumstance that the secretion of urea from the body 
(and consequently the loss of nitrogen) goes on continually, 
whether the body is fed or not : while there is only one form in 
which nitrogen (at any rate, in any considerable quantity) can 
be taken into the blood, and that is in the form of a solution 
of protein. If protein be not supplied, therefore, the body 
must needs waste, because there is nothing in the food compe- 
tent to make good the loss of nitrogen. 

On the other hand, if protein be supplied there can be no 
absolute necessity for any other but the mineral food-stuifs, be- 
cause protein contains carbon and hydrogen in abundance, and 
hence is competent to give origin to the other great products 
oi waste, carbonic acid and water. 

In fact, the final results of the oxidation of protein are car- 
bonic acid, water, and ammonia; and these, as we have seen, are 
the final shapes of the waste products of the human economy. 

179. Nitrogen Starvation. — From what has been said, it 
becomes readily intelligible that whether an animal be herbiv- 
orous or carnivorous, it begins to starve from the moment its 
vital food-stufis consist of pure amyloids or fats, or any mixture 
of them. It suffers from what may be called nitrogen starva- 
tion^ and, sooner or later, will die. 

In this case, and still more in that of an animal deprived 
of vital food altogether, the organism, so long as it continues to 
live, feeds upon itself, and its excretions are all necessarily 
formed at the expense of its own body ; whence it has been 
rightly enough observed that a starving sheep is as much a 
carnivore as a lion. 

180. Disadvantages of a purely Nitrogenous Diet. — 
But though protein is the essential element of food, and under 



PROPERTIES OF FOOD-STUFFS. 137 

certain circumstances may suffice, by itself, to maintain the 
body, it is a very disadvantageous and uneconomical food. 

Albumen, wbicli may be taken as the type of the proteids, 
contains about 53 parts of carbon and 15 of nitrogen in 100 
parts. If a man were to be fed upon white of egg^ therefore, 
he would take in, speaking roughly, 3j parts of carbon for 
every part of nitrogen. 

But it is proved experimentally, that a healthy fulbgrown 
man, keeping up his weight and heat, and taking a fair amount 
of exercise, eliminates 4,000 grains of carbon to only 300 grains 
of nitrogen, or, roughly, only needs one-thirteenth as much 
nitrogen as carbon. However, if he is to get his 4,000 grains 
of carbon out of albumen, he must eat 7,547 grains of that sub- 
stance. But 7,547 grains of albumen contain 1,132 grains of 
nitrogen, or nearly four times as much as he wants. 

To put the case in another way, it takes about four pounds 
of fatless meat to yield 4,000 grains of carbon, whereas one 
pound will furnish 300 grains of nitrogen. 

Thus a man confined to a purely proteid diet, must eat a 
prodigious quantity of it. This not only involves a great 
amount of physiological labor in comminuting the food, and a 
great expenditure of power and time in dissolving and absorb- 
ing it; but throws a great quantity of wholly profitless labor 
upon those excretory organs, which have to get rid of the nitro- 
genous matter, three-fourths of which, as we have seen, is super- 
fluous. 

181. Economy of Physiological Power. — Unproductive 
labor is as much to be avoided in physiological, as in political, 
economy ; and it is quite possible that an animal fed with per- 
fectly nutritious protein matter should die of starvation, the loss 
of power in the various operations required for its assimilation 
overbalancing the gain ; or the time occupied in their perform- 
ance being too great to check waste with sufficient rapidity. 
The body, under these circumstances, falls into the condition 
of a merchant who has abundant assets, but who cannot got in 
his debts in time to meet his creditors. 



138 ELEMENTARY PHYSIOLOGY. 

182. Economy of a Mixed Diet. — These considerations 
lead us to the physiological justification of the universal prac- 
tice of mankind in adopting a mixed diet, in which proteids 
are mixed either with fats, or with amyloids, or with both. 

Fats may be taken to contain about 80 per cent, of carbon, 
and amyloids about 40 per cent. Now it has been seen that 
there is enough nitrogen to supply the waste of that substance 
per diem, in a healthy man, in a pound of fatless meat ; which 
also contains 1,000 grains of carbon, leaving a deficit of 3,000 
grains of carbon. Rather more than half a pound of fat, or a 
pound of sugar, will supply this quantity of carbon. The 
former, if properly subdivided, the latter, from its solubility, 
passes with great ease into the economy, the digestive labor 
of which is consequently reduced to a minimum. 

183. Advantages of a Mixed Diet. — Several apparently 
simple articles of food constitute by themselves a mixed diet. 
Thus butcher's meat commonly contains fi'om 30 to 50 per 
cent, of fat. Bread, on the other hand, contains the proteid, 
gluten, and the amyloids, starch and sugar, with minute quan- 
tities of fat. But, from the proportion in which these proteid 
and other constituents exist in these substances, they are 
neither, taken alone, such physiologically economical foods, as 
when they are combined in the proportion of about 200 to 75 ; 
or two pounds of bread to three-quarters of a pound of meat 
per diem, 

184. Intermediate Changes of the Food. — It is quite 
certain that nine-tenths of the dry solid food w^hich is taken 
into the body, sooner or later leaves it in the shape of carbonic 
acid, water, and urea (or uric acid) ; and it is also certain that, 
as the compounds which leave the body are more highly oxi- 
dated than those which enter it, and as free oxygen is nowhere 
eliminated, all the oxygen taken in by the lungs passes away 
in these compounds. 

The intermediate stages of this conversion are, however, 
by no means so clear. It is highly probable that the amyloids 
and fats are very frequently oxidated in the blood, without, 



PKOPERTIES OF FOOD-STUFFS. 139 

properly speaking, ever forming an integral part of the sub- 
stance of the body ; but whether the proteids may undergo the 
same changes in the blood, or whether it is necessary for them 
first to be incorporated with the living tissue, is not positively 
known. 

So, again, it is certain that, in becoming oxidated, the ele- 
ments of the food must give off heat, and it is probable that 
this heat is sufficient to account for all that passes off by the 
body ; but it is possible, and indeed probable, that there may 
be other, minor, sources of heat. 

185. Objections to the Commoii Classification. — Food- 
stuffs have been divided into heat-producers and tissue-formers — 
the amyloids and fats constituting the former division, the pro- 
teids the latter. But this is a very misleading classification, 
inasmuch as it implies, on the one hand, that the oxidation of 
the proteids does not develop heat ; and, on the other, that the 
amyloids and fats, as they oxidize, subserve only the produc- 
tion of heat. 

Proteids are tissue-formers^ inasmuch as no tissue can be 
produced without them ; but they are also heat-producers^ not 
only directly, but because, as we have seen, they are compe- 
tent to give rise to amyloids by chemical metamorphosis within 
the body. 

If it is worth while to make a special classification of the 
vital food-stufls at all, it appears desirable to distinguish the 
essential food-stuffs, or proteids, from the accessory food-stuff's, 
or fats and amyloids — the former alone being, in the nature 
of things, necessary to life, while the latter, however important, 
are not absolutely necessary. 

186. Purpose of the Alimentary Mechanism.— All food- 
stuflfs being thus proteids, fats, amyloids, or mineral matters, 
pure or mixed up with other substances, the whole purpose 
of the alimentary apparatus is to separate these proteids, etc., 
from the innutritions residue, if there be any; and to reduce 
them into a condition either of solution or of excessively ^no 
subdivision, in order that they may make their way through 



140 ELEMENTARY PHYSIOLOGY. 

the delicate structures which form the walls of the vessels of 
the alimentary canal. To these ends food is taken into the 
mouth and masticated, is insalivated, is swallowed, undergoes 
gastric digestion, passes into the intestine, and is subjected to 
the action of the secretions of the glands attached to that 
viscus ; and, finally, after the more or less complete extraction 
of the nutritive constituents, the residue, mixed up with cer- 
tain secretions of the intestine, leaves the body as the fceces. 

Section II. — Pi^eliminaries of Digestion, 

187. The Mouth and Pharynx. — The cavity of the mouth 
is a chamber with a fixed roof, formed by the hard palate (Fig. 
53, Z), and with a movable floor, constituted by the low^er jaw, 
and the tongue (^), which fills up the space between the two 
branches of the jaw. Arching round the margins of the upper 
and the lower jaws are the thirty-two teeth, sixteen above and 
sixteen below, and, external to these, the closure of the cavity 
of the mouth is completed by the cheeks, at the sides, and by 
the lips, in front 

When the mouth is shut, the back of the tongue comes 
into close contact with the palate; and, where the hard palate 
ends, the communication between the mouth and the back of 
the throat is still further impeded by a sort of fleshy curtain — 
the soft palate, or velum — the middle of which is produced into 
a prolongation, the uvula (/), while its sides, skirting the sides 
of the passage, ov fauces, are double muscular pillars, which are 
termed the pillars of the fauces. Between these the tonsils are 
situated, one on each side. 

The velum with its uvula comes into contact below with 
the upper part of the back of the tongue, and with a sort of 
gristly lid-like process connected with its base, the epiglottis {e). 

Behind the partition thus formed is the cavity of the 
pharynx, which may be described as a funnel-shaped bag with 
muscular w^alls, the upper margins of the wide end of which 
are attached to the base of the skull, while its lateral margins 



PKELIMINARIES OF DIGESTIOiiq^. 



141 



are continuous with the walls of the cheeks, and the lower walls 
with the floor of the mouth. The narrow end of the pharyn- 
geal hag passes into the gullet or (esophagus (6), a muscular- 
walled tube, which affords a passage into the stomach. 




Fig. 58. 

A section of the mouth and nose, taken vertically, a little to the left of the middle 
line— a, the vertebral column; &, the gullet; c, the windpipe; d, the thyroid 
cartilaf^e of the larnyx; e^ the epiglottis; /, the uvula; </, the opening of the left 
Eustachian tube; h, the opening of the left lachrymal duct; ?, the hyoid bone; 
k% the tongue ; Z, the hard palate; m n, the base of the skull ; o p q, the superior, 
middle, and inferior turbinal bones. The letters gfe, are placed in the pharynx. 

There are no fewer than six distinct openings into the 
pharynx — four in pairs, and two single ones in the middle line. 
The two pairs are, in front, the hinder openings of the nasal 
cavities. At the sides, close to these, are the apertures of the 
Eustachian tubes ((/), The two single apertures are, the hinder 
opening of the mouth between the soft palate and the epiglottis ; 



142 ELEMENTARY PHYSIOLOGY. 

and, behind the epiglottis, the upper aperture of the respiratory 
passage, or the glottis, 

188. The Salivary Glands. — The mucous membrane which 
lines the mouth and the pharynx is beset with minute glands, 
the buccal glands ; but the great glands from which the cavity 
of the mouth receives its chief secretion, are the three pairs 
which, as has been already mentioned, are called parotid, sub- 
maxillary^ sublingual, and which secrete the saliva. (Fig. 54.) 

Each parotid gland is placed just in front of the ear, and 
its duct passes forward along the cheek, until it opens in its in- 
terior, opposite the second upper grinding tooth. 

The submaxillary and sublingual glands lie between the 
lower jaw and the floor of the mouth, the submaxillary farther 




Fig. 54. 

A dissection of tLe right side of the face, showing, a, the sublingual; 5, the submax- 
illary glands, with their ducts opening beside the toneue in the floor of the month 
at d ; c, the parotid gland and its ducF, which opens on the side of the cheek at e, 

back than the sublingual. Their ducts open in the floor of the 
mouth below the tip of the tongue. The secretion of these, 
mixed with that of the small glands of the mouth, constitutes 
the saliva — a fluid which, though thin and watery, contains a 
small quantity of animal matter, which has certain very peculiar 
properties. It docs not act upon proteid food-stuffs, nor upon 
fats, but if mixed with starch and kept at a moderately warm 



PRELIMIISrARIES OF DIGESTIOIST. 143 

temperature, it turns that starch into grape-sugar. The im- 
portance of this operation becomes apparent when one reflects 
that starch is insoluble and useless as nutriment, while sugar is 
highly soluble and readily oxidable. 

189. The Teeth. — Each of the thirty -two teeth which have 
been mentioned consists of a crown which projects above the 
gum, and of one or more fangs, which are imbedded in sockets, 
or what are called alveoli^ in the jaws. 

The eight teeth on opposite sides of the same jaw are con- 
structed upon exactly similar patterns, while the eight teeth 
which are opposite to one another, and bite against one another 
above and below, though similar in kind, differ somewhat in 
the details of their patterns. 

The two teeth in each eight which are nearest the middle 
line in the front of the jaw, have wide but sharp and chisel-like 
edges. Hence they are called incisors, or cutting teeth. The 
tooth which comes next is a tooth with a more conical and 
pointed crown. It answers to the great tearing and holding 
tooth of the dog, and is called the canine or eye tooth. The 
next two teeth have broader crowns, with two cusps or points 
on each crown, one on the inside and one on the outside, 
whence they are termed bicuspid teeth, and sometimes false 
grinders. 

All these teeth have usually one fang each, except the 
bicuspid, the fang of which may be more or less completely 
divided into two. The remaining teeth have two or three 
fangs each, and their crowns are much broader. As they 
crush and grind the matters which pass between them, they 
are called molars^ or true grinders. In the upper jaw their 
crowns present four points at the four corners and a diagonal 
ridge connecting two of them. In the lower jaw the complete 
pattern is five-pointed, there being two cusps on the inner side 
and three on the outer. 

190. Working of the Jaw. — The muscles of the parts 
which have been described are so arranged that the lower jaw 
can be depressed to open the mouth and separate the teeth, or 



144: ELEMENTARY PHYSIOLOGY. 

raised in such a manner as to bring the teeth together, or 
moved obliquely from side to side, so as to cause the face of 
the grinding teeth and the edges of the cutting teeth to sUde 
over one another. And the muscles which perform the ele- 
vating and sliding movements are of great strength, and con- 
fer a corresponding force upon their grinding and cutting 
movements. In correspondence with the pressure they have 
to resist, the superficial substance of the crown of the teeth is 
of great hardness, being foniied of enamel, the hardest sub- 
stance in the body, so dense and hard, indeed, that it wall 
strike fire with steel. But notwithstanding its extreme hard- 
ness, it becomes worn down in old persons, and at an earlier 
age in savages who live on coarse food. 

191. Masticating and SwaUowing. — When solid food is 
taken into the mouth it is cut and ground by the teeth, the 
fragments wiiich ooze out upon the outer side of their crowns 
being pushed beneath them again by the muscular contrac- 
tions of the cheeks and lips, while those which escape on the 
inner side are thrust back by the tongue, until the whole is 
thoroughly rubbed down. 

While mastication is proceeding, the salivary glands pour 
out their secretion in great abundance, and the saliva mixes 
Avith the food, which then becomes interpenetrated not only 
with the salivary fluid, but with the air which is entangled 
in the bubbles of the saliva. 

When the food is sufficiently ground it is collected, en- 
veloped in saliva, into a mass or bolus, which rests upon the 
back of the tongue, and is carried backward to the aperture 
which leads into the pharynx. Through this it is thrust, the 
soft palate being lifted and its pillars being brought together, 
Avhile the backward movement of the tongue at once propels 
the bolus and causes the epiglottis to incline backward and 
downward over the glottis, and so to form a bridge by which 
the bolus can travel over the opening of the air-passage with- 
out any risk of tumbling into it. While the epiglottis directs 
the course of the bolus below and prevents it from passing 



PEELIMIJSrATlIES OF DIGESTION". 145 

into the trachea, the soft palate guides it above, keeps it out 
of the nasal chamber, and directs it downward and backward 
toward the lower part of the muscular pharyngeal funnel. 
By this it is immediately seized and tightly held, and 'the 
muscular fibres contracting above it, while they are compara- 
tively lax below, it is rapidly thrust into the oesophagus, 
grasped by it, and propelled along it, in the same way, until 
it reaches tbe stomach. 

192. Drinking. — Drink is taken in exactly the same w^ay. 
It does not fall down the pharynx and gullet, but each gulp 
is grasped by it and passed down. Hence it is that jugglers 
are able to drink standing upon their heads, and that a horse, 
or ox, drinks with its throat lower than its stomach, feats 
which would be impossible if fluid simply fell down the gullet 
into the gastric cavity. 

During these processes of mastication, insalivation, and deg- 
lutition, what happens to the food is, first, that it is reduced 
to a coarser or finer pulp; secondly, that any matters it 
carries in solution are still more diluted by tbe water of the 
sahva; thirdly, that any starch it may contain begins to be 
changed into sugar by the peculiar constituent (ptyalin) of the 
saliva. 

Section III. — Stomach-Digestion, 

193. The Stomach and the Gastric Juice.— The stomach, 
like the gullet, consists of a tube with muscular w^alls com- 
posed of smooth muscular fibres, and lined by an epithelium ; 
but it differs from the gullet in several circumstances. In the 
first place, its cavity is greatly laro'or, and its left end is pro- 
duced in^o an enlargement which, because it is o'l the heart 
side of the body, is called tbe cardiac dilatation (Fig. 55, h\ 
The opening of the gullet into tlie stomach, termed the carJiac 
aperture, is consequently nearly in the middle oi the whole 
length of the organ, which presents a long, convex, greater 
curvature, along its front or under edge, and a short concave, 

7 



14:6 ELEMENTARY PHYSIOLOGY. 

lesser curvature, on its back or upper contour. Toward its 
right extremity the stomach narrows, and, where it passes into 
the intestine, the muscular fibres are so disposed as to form a 
sort of sphincter around the aperture of communication — the 
pylorus (Fig. 55, d). 




Fig. 55. 

The stem ach laid open behind — a. the cesophasrus; 5, the cardiac dilatation; e, the 
lesser curvature ; 6?, the pylorus; e, the biliary duct ;/; the gall-bladder; ^, the 
pancreatic duct, opening In common witb the cystic duct opposite h\ A, i, the 
duodenum. 

The mucous membrane Hning the wall of the stomach is 
very delicate, and multitudes of small simple glands open upon 
its surface. Among these are others (Fig. bQ) which possess a 
somewhat more complicated structure, their blind ends being 
subdivided. It is these peptic glaiids which, when food passes 
into the stomach, throw out a thin acid fluid, the gastric juice. 
The acidity arises from the presence of lactic or hydrochloric 
acids, but in addition to these constituents the gastric juice 
possesses another called pepsin, which appears to be a protein 
compound not altogether dissimilar to ptyalin. 

Thus, when the food passes into the stomach, the contrac- 
tions of that organ roll it about and mix it thoroughly with 
the gastric juice. 



STOMACH-DIGESTIOlSr. 



147 



194. Artificial Digestion. — It is easy to ascertain ex- 
perimentally the properties of the gastric juice by putting a 
small portion of that part of the mucous membrane which 




Fig. 56. 
One of the glands which secrete the gastric juice highly magnified. 

contains the peptic glands into water containing small pieces 
of meat, hard-boiled eggj or other proteids, and keeping 
the mixture at a temperature of about 100°. After a few 
hours it will be found that the white of egg has become dis- 
solved, if not in too great quantity, while all that remains of 
the meat is a pulp consisting chiefly of the connective tissue 
and fatty matters which it contained. This is artificial diges- 
tion, and it has been proved by experiment that precisely the 
same operation takes place when food undergoes natural di- 
gestion within the stomach of the living animal. 

The proteid solution thus eftected is called a peptone, and 



148 ELEMENTARY PHYSIOLOGY. 

has pretty rauch the same characters, whatever the nature of 
the proteid which has been digested. 

The dilute acid alone is competent slowly to dissolve the 
proteid, but the pepsin in the gastric juice is the chief source 
of its soh^ent power. 

195. Absorption from the Stomach. — By continual roll- 
ing about, with constant additions of gastric juice, the food 
becomes reduced to the consistence of pea-soup, and is called 
chyme. In this state it is, in part, allowed to escape through 
the pylorus and to enter the duodenum, but a great deal of the 
fluid (consisting of peptone mixed with saliva and any saccha- 
rine fluids resulting from the partial conversion of starch or 
otherwise) is at once absorbed, making its way, by imbibition, 
through the walls of the delicate and numerous vessels of the 
stomach into the current of the blood, which is rushing by the 
gastric veins to the vena portce. 

Section IV. — Intestinal Digestion, 

196. The Large and Small Intestines. — The intestines 
form one long tube, with mucous and muscular coats, like the 
stomach ; and like it they are enveloped in peritoneum. They 
are divided into two portions — the small intestines and the 
large intestines^ the latter having a much greater diameter than 
the former. The small intestines again are subdivided into the 
duodenum^ the jejunum^ and the ileum^ but there is no natural 
line of demarcation between these. The duodenum, however, 
is distinguishable as that part of the small intestine which im- 
mediately succeeds the stomach, and is bent upon itself and 
fastened by the peritoneum against the back wall of the abdo- 
men in the loop shown in Fig. 55. It is in this loop that the 
head of the pancreas lies (Fig. 50). 

The ileum (a, Fig. 57) is no wider than the jejunnm or 
duodenum, so that the transition from the small intestine to 
the large (e) is quite sudden. The opening of the small in- 
testine into the large is provided with prominent lips which 



INTESTINAL DIGESTION. 149 

project into the cavity of the former and oppose the passage 
of matters from it into the small intestine, while they readily 
allow of a passage the other way. This is the ileo-ccecal 
valve. 

The large intestine forms a blind dilatation beyond the 
ileo-csecal valve, which is called the cceciim ; and from this an 
elonp-ated blind process is given off, which, from its shape, is 
called the vermiform appendix of the csecum (Fig. 57, 6). 

The csecum lies in the lower part of the right side of the 
abdominal cavity. The colon^ or first part of tbe large intes- 
tine, passes upward from it as the ascending colon ; then making 
a sudden turn at a right angle, it bends across to the left side 
of the body, being here called transverse colon, and next, sud- 




FiG. 57. 

The termination of the ilonm, a, in the c.TCiim, and the continuation of the latter 
into the colon, c; d, the ilco-colic valve; e^ the aperture of the (ipjyendix vermi- 
forinis (b) into the caecum. 

denly bending backward along the left side of the abdomen, 
becomes the descending colon. This reaches the middle line 
and becomes the rectum, which is that part of the large intes- 
tine which opens externally. 

197. Their Parts and Actions. — The mucous membrane 
of the whole intestine is provided with nnmerous small, and for 
the most part siniplo, glands (named after Lieberkiilin and 
Brunncr), which pour into it a secretion, the intestinal juice, 
the precise functions of which are imknown. 



150 



ELEMENTARY PHYSIOLOGY. 



Structures peculiar to the small intestine are the valvulce 
conniventeSj transverse folds of the mucous membrane, which 
increase the surface; and the villi, which are minute thread- 
like processes of the mucous membrane on the valvulce conni- 
ventes and elsewhere, set side by side, like the pile of velvet. 




Fig. 58. 

Two villi of the small intestines— a, substance of the villus; 5, its epithelium, of 
which some cells are seen detached at b^ ; c c?, the artery and vein, with their 
connecting capillary net-work, which envelops and hides, e, the lacteal radicle 
which occupies the centre of the villus and opens into a net-work of lacteal ves- 
sels at its base. 



Each villus is coated by epithelium and contains in its interior 
the radicle, or commencement, of a lacteal vessel, between 
which and the surface of the villus lies a capillary net-work 
with its afferent artery and efferent vein. 

Peculiarities of the large intestine are the arrangement of 
the longitudinal muscular fibres of the colon into three bands, 
which are shorter than the walls of the intestine itself, so that 
the latter is thrown into puckers and pouches ; and the disposi- 
tion of muscular fibres around the termination of the rectum 
into a ring-like sphincter muscle, which keeps the aperture 
firmly closed, except when defecation takes place. 

The intestines receive their blood almost directly from the 
aorta. Their veins carry the blood which has traversed them 
to the vena portce. 



INTESTINAL DIGESTION. 151 

198. Peristaltic Contraction.— The fibres of tlie muscular 
coat of the intestine, which lies between its mucous membrane 
and its serous, or peritoneal, investment, are disposed longitu- 
dinally and circularly, and the circular fibres of any part con- 
tract, successively, in such a manner that the lower fibres, or 
those on the side of the anus, contract after the upper ones, or 
those on the side of the pylorus. It follows from this so-called 
peristaltic contraction, that the contents of the intestines are 
constantly being propelled, by successive waves of contraction, 
from their upper toward their lower parts. 

199. Entrance of Bile and Pancreatic Juice.— The only 
secretions besides those of the proper intestinal glands which 
enter the intestine, are those of the liver and the pancreas — 
the bile and the pancreatic juice. The ducts of these organs 
have a common opening in the middle of the bend of the duo- 
denum ; and, since they pass obliquely through the coats of the 
intestine, their aperture serves as a kind of valve, obstructing 
the flow of fluid from the duodenum, but permitting its passage 
to the duodenum (Figs. 50 and 55). 

As the chyme fills the duodenum, the pancreas comes into 
activity, and its secretion, with the bile from the gall-bladder, 
flows through the common aperture, and, mixing with the chyme, 
converts it into what is called chyle. 

200. Chyle — Absorption from the Intestines. — Chyle 
differs irom chyme in two respects. In the first place, the 
alkali of the bile neutraUzes the acid of the chyme ; in the 
second place, both the bile and the pancreatic juice appear to 
exercise an influence over the fatty matters contained in the 
chyme, which facilitates the subdivision of these fats into very 
minute separate particles. The chyme, in fact, which results 
from the digestion of fatty food, is mere mixture of watery fluid 
with oily matters which are ready to separate from it and unite 
with one another. In the chyle, on the other hand, the fatty 
matters arc suspended in the fluid, just as oil may bo evenly 
diffused through water by gradually rubbing it up with white 
of Q.gg into what is termed an emulsion,, or as the lat ( = butter) 



152 ELEMENTARY PHYSIOLOGY. 

of milk is naturally held suspended in the watery basis of 
milk. 

The chyle, with these suspended particles, looks white and 
milky, for the same reason that milk has the same aspect— the 
muhitude of minute suspended fatty particles reflecting a great 
amount of liivht. 

o 

The conversion of starch into sugar, which seems to be sus- 
pended wholly, or partially, so long as the food remains m the 
stomach, on account of the acidity of the chyme, is resumed 
as soon as the latter is neutralized, the pancreatic and intestinal 
juices operating powerfully in this direction. 

As the chyle is thrust along the small intestines by the 
grasping action of the peristaltic contractions, the dissolved 
matter which it contains is absorbed, in the ordinary way, by 
the vessels of the villi. The minute particles of fatty matter, on 
the other hand, are squeezed through the soft substance of the 
epithelium into that of the villi; and so, in the long run, mto 
the vessels; just as mercury may be squeezed by pressure 
through the pores of a wash-leather bag. 

As the net-work of capillaries lies outside the lacteal radicle 
in each villus, it would appear that the blood-vessels must carry 
off the greater part of the chyle ; but much of it enters the lac- 
teals, fills them, and only enters the blood after a roundabout 
passage through the mesenteric lymphatics and the thoracic 
duct. 

201. Digestion in the Large Intestines. — The digested 
matters, as they are driven along the small intestines, gradually 
become deprived of their peptones, fats, and soluble amyloids, 
and are forced through the ileo-ca3cal valve into the caecum and 
large intestine. Here they acquire an acid reaction and the 
characteristic fecal odor and color, which become more and 
more marked as they approach the rectum. It has been sup- 
posed that a sort of second digestion occurs in the upper part 
of the large intestine. 



mSTEUMENTS OF MOTION, 153 

CHAPTER VIIL 

MOTION AND LOCOMOTION. 

Section I. — Instruments of Motion, 

202. The Vital Eddy. — In the precediDg pages we have 
studied the manner in which the incomings of the human body 
are converted into its outgoings. We have seen that matter, 
in the form of vital and mineral foods, is constantly appro- 
priated by the bodj, to make up for the loss of matter, in the 
shape, chiefly, of carbonic acid, urea, and water, which is as 
constantly going on. The vital foods are derived directly, or 
indirectly, from the vegetable world; and the products of waste 
either are such compounds as abound in the mineral world, 
or immediately decompose into them. Consequently, the 
human body is the centre of a stream of matter which sets 
incessantly from the vegetable and mineral worlds into the 
mineral world again. It may be compared to an eddy in a 
river, wdiich may retain its shape for an indefinite length of 
time, though no one particle of the water of the stream re- 
mains in it for more than a brief period. 

But there is this peculiarity about the human eddy, that a 
large portion of the particles of matter which flow into it have 
a much more complex composition than the particles which 
flow out of it. To speak in what is not altogether a metaphor, 
a large part of the atoms which enter the body are piled up 
in large heaps, and tumble down into small heaps before they 
leave it. The force which they set free in thus tumbling down, 
is the source of the active powers of the oro-anism. 

203. Organs of Motion. — These active powers are chiefly 
manifested in the form of motion — movement, that is, either 
of part of the body, or of the body as a whole, which last is 
termed locomotion. 

7* 



154 ELEMENTARY PHYSIOLOGY. 

The organs which produce motion in the human body are 
of two kinds: Cilia and Muscles, 

204. Action of the Cilia. — Cilia are filaments of extremely 
small size, attached by their bases to, and indeed growing out 
from, the free surfaces of epithelial cells. They are in inces- 
sant waving motion, so long as life persists in them ; and the 
motion of a cilium continues even for some time after the 
epithelial cell, with which it is connected, is detached from the 
body. Not only does the movement of the cilia thus go on 
independently of the rest of the body, but it cannot be con- 
trolled by the action of the nervous system. The cause of the 
movement of each cilium would appear to be the alternate con- 
traction and relaxation of opposite sides of its base ; but why 
these alternations take place is unknown. 

Although no other part of the body has any control over 
the cilia, and though, so far as we know, they have no direct 
communication with one another, yet their action is directed 
toward a common end — the cilia, which cover extensive sur- 
faces, all working in such a manner as to sweep whatever lies 
upon that surface in one and the same direction. Thus, the 
cilia which are developed upon the epithelial cells which line 
the greater part of the nasal cavities and the trachea with its 
ramifications, tend to drive the mucus in which they work, 
outward. 

In addition to the air-passages, cilia are found, in the hu- 
man body, in the ventricles of the brain, and in one or two 
other localities ; but the part which they play in man is insig- 
nificant in comparison with their function in the lower animals, 
among many of which they become the chief organs of loco- 
motion. 

205. Muscular Contraction. — Muscles are accumulations 
of fibres, each of which has the power, under certain condi- 
tions, of shortening in lencrth, while it increases its other di- 
mensions, so that the absolute volume of the fibre remains 
unchanged. This power is called 7nuscular contractility/ ; and 
whenever a muscular fibre contracts, in virtue of this power, it 



INSTRUMENTS OF MOTION. 155 

tends to bring its two ends, with whatever may be fastened to 
them, together. 

Muscles may be conveniently divided into two groups, ac- 
cording to the manner in which the ends of their fibres are 
fastened; into muscles not attached to solid levers, and muscles 
attached to solid levers. 

206, Hollow Muscles not attached to Solid Levers. — The 
muscles which come under this head are what are, sometimes, 
appropriately called hollow muscles, inasmuch as they enclose 
a cavity, or surround a space ; and their contraction produces 
a diminution in the capacity of that cavity, or the extent of 
that space. 

The muscular fibres of the heart, of the blood-vessels, of the 
lymphatic vessels, of the alimentary canal, of the ducts of the 
glands, of the iris of the eye, are so arranged as to form hollow 
muscles. 

In the heart the muscular fibres are of the striated kind 
(see Chapter XIIL), and their disposition is exceedingly com- 
plex. The cavities which they enclose are those of the auri- 
cles and ventricles ; and, as we have seen, the fibres, when they 
contract, do so suddenly and together. 

The iris of the eye is like a curtain, in the middle of which 
is a circular hole. The muscular fibres are not striated (see 
Chapter XITT.), and they are disposed in two ways : some radi- 
ating from the edges of the hole to the circumference of the 
curtain ; some arranged in circles, concentrically with the 
aperture. The muscular fibres contract suddenly and together, 
the radiating fibres necessarily enlarging the hole, the circular 
fibres diminishing it. 

In the alimentary canal the muscular fibres are also of the 
unstriated kind, and they are disposed in two layers ; one set 
of fibres arranged parallel with the length of the intestines, the 
others being disposed circularly, or at right angles to the 
I former. 

The contraction of these muscular fibres is successive ; that 
is to say, all the muscular fibres, in a given length of the in- 



156 ELEMENTARY PHYSIOLOGY. 

testines, do not contract at once, but those at one end contract 
first, and tlie others follow them until the whole series have 
contracted. As the order of contraction is, naturally, always 
the same, from the upper toward the lower end, the effect of 
this peristaltic contraction is, as we have seen, to force any 
matter contained in the ahmentary canal, from its upper tow- 
ard its low^er extremity. The muscles of the walls of the 
ducts of the glands, have a substantially similar arrangement 

Section 11.— Mechanism of Bodily Movement 

207. Muscles attached to Definite Levers. — The great 

majority of the muscles of the body are attached to distinct 
levers, formed by the bones; and to understand their action, 
we must have a knowledge of the different kinds of levers, and 
be able to refer the various combinations of the bones to their 
appropriate lever-classes. 

A lever is a rigid bar, one part of which is absolutely or 
relatively fixed, while the rest is free to move. Some one point 



"vv ^^ p ^ w 





Fig. 59. Fig. 60. Fig. 61. 

The upper three figures represent the three kinds of levers: the lower, the foot, when 
it takes the character of each kind. — W. Weight or resistance; F. fulcrum; P. 
power. 

of the movable part of the lever is set in motion by a source 
of power, in order to communicate more or less of that motion 
to another JDoint of the movable part, which presents a resist- 
ance to motion in the shape of a weight or other obstacle. 

203. Three Orders of Levers. — Three kinds of levers are 
enumerated by mechanicians, the definition of each kind de- 



MECHANISM OF BODILY MOVEMENT. 157 

pending upon the relative positions of the point of support, or 
fulcrum ; of the point which bears the resistance^ weighty or 
other obstacle to be overcome by the power ; and of the point 
to w^hich the source of poioer employed to overcome the ob- 
stacle is applied. 

If the fulcrum be placed between the power and the weight, 
so that when the power sets the lever in motion, the weight 
and the power describe arcs, the concavities of which are turned 
toward one another, the lever is said to be of the first order 
(Fig. 59). 

If the fulcrum be at one end, and the weight be between it 
and the power, so that weight and power describe concentric 
arcs, the weight moving through the less space when the lever 
moves, the lever is said to be of the second order (Fig. 60). 

And if, the fulcrum being still at one end, the power be 
between the weight and it, so that, as in the former case, the 
power and weight describe concentric arcs, but the power 
moves through the less space, the lever is of the third order 
(Fig. 61). 

209. Levers of the First Ordero— In the human body, the 
following parts present examples of levers of the first order. 

(a) The skull in its movements upon the atlas, 2i^ fulcrum. 

(b) The pelvis in its monements upon the heads of the 
thigh-bones, as fulcrum. 

(c) The foot, when it is raised, and the toe tapped on the 
ground, the ankle joint heiug fulcrum (Fig. 59). 

I have not given the position of the weight and power in 
either of these cases, because they are reversed according to 
circumstances. Thus, when the face is being depressed, the 
power is applied in front, and the weight to the back part, of 
the skull ; but when the foce is being raised, the power is bo- 
hind and the weight in front. The like is true of the pelvis, 
according as the body is bent forward, or backward, upon the 
legs. Finally, when the toes, in the action of tapping, strike 
the ground, the power is at the heel, and the resistance in the 
front of the foot. But, when the toes are raised to repeat the 



158 ELEMENTAEY PHYSIOLOGY. 

act, the power is in front, and the weight, or resistance, is at 
the heel, being, in fact, the inertia and elasticity of the muscles 
and other parts of the back of the leg. 

But, in all these cases, the lever remains one of the first 
class, because the fulcrum, or fixed point on which the lever 
turns, remains between the power and the weight, or resistance. 

210. Levers of the Second Order. — The following are three 
examples of levers of the second order : 

(a) The thigh-bone of the leg which is bent up toward the 
body and not used, in the action of hopping. 

For, in this case, the fulcrum is at the hip-joint. The 
power (which I assume to be furnished by the rectus muscle of 
the front of the thigh) acts upon the knee-cap; and the posi- 
tion of the weight is represented by that of the centre of grav- 
ity of the thigh and leg, which will lie somewhere between the 
end of the knee and the hip. 

(6) A rib when depressed by the rectus muscle of the ab- 
domen, in expiration. 

Here the fulcrum lies where the rib is articulated with the 
spine ; the power is at the sternum — virtually the opposite end 
of the rib ; and the resistance to be overcome lies between the 
two. 

(c) The raising of the body upon the toes, in standing on 
tiptoe, and in the first stage of making a step forward 
(Fig. 60). 

Here the fulcrum is the ground on which the toes rest ; the 
power is applied by the muscles of the calf to the heel; the 
resistance is so much of the weight of the body as is borne by 
the ankle-joint of the foot, which of course lies between the 
heel and the toes. 

211. Levers of the Third Order. — Three examples of 
levers of the third order are — 

(a) The spine, head, and pelvis, considered as a rigid bar, 
which has to be kept erect upon the hip-joints (Fig. 4). 

Here the fulcrum lies in the hip-joints ; the weight is at 
the centre of gravity of the head and trunk, high above the 



MECHANISM OF BODILY MOVEMENT. 159 

fulcrum ; the power is supplied by the extensor, or flexor, 
muscles of the thigh, and acts upon points comparatively close 
to the fulcrum. 

[h) Flexion of the forearm upon the arm by the biceps 
muscle, when a weight is held in the hand. 

In this case, the weight being in the hand and the fulcrum 
at the elbow-joint, the power is applied at the point of attach- 
ment of the tendon of the biceps, close to the latter. 

(c) Extension of the leg on the thigh at the knee-joint. 

Here the fulcrum is the knee-joint ; the weight is at the 
centre of gravity of the leg and foot ; the power is applied by 
the ligament of the knee-cap, or patella, to the tibia, close to 
the knee-joint. 

212. One Part may represent the Three Kinds. — In 
studying the mechanism of the body, it is very important to 
recollect that one and the same part of the body may represent 
each of the three kinds of levers, according to circumstances. 
Thus it has been seen that the foot may, under some circum- 
stances, represent a lever of the first, in others of the second 
order. But it may become a lever of the third order, as when 
one dances a weight resting upon the toes, up and down, by 
moving only the foot. In this case, the fulcrum is at the 
ankle-joint, the weight is at the toes, and the powder is fur- 
nished by the extensor muscles at the front of the leg, which 
are inserted between the fulcrum and the weight (Fig. 61). 

213. Different Kinds of Joints. — It is very important that 
the levers of the body should not slip, or work unevenly, when 
their movements are extensive, and to this end they are con- 
nected together in such a manner as to form strong and defi- 
nitely arranged yom^5 or articulations, 

(a) Imperfect joints are those in which the conjoined levers 
(bones or cartilages) present no smooth surfaces, capable of 
rotatory motion, to one another, but arc connected by contin- 
uous cartilages, or ligaments, and have only so much mobility 
as is permitted by the flexibility of the joining substance. 

Examples of such joints as these are to be met with in the 



160 



ELEMENTARY PHYSIOLOGY. 



vertebral column — the flat surfaces of the several joints, or ver- 
tebrae, being connected together by thick plates of very elastic 
fibro-cartilage, which confer upon the whole column consid- 
erable play and springiness, and yet prevent any great amount 
of motion between the several vertebrae. The pubic bones are 
united together, and the haunch-bones with the sacrum, by 
fibrous or cartilaginous tissue, which allows of only a slight 
play, or may merely confer a little more elasticity than if the 
joint were formed by the direct apposition of bones. 

214. Structure and Working of Joints. — In all perfect 
joints, the opposed surfaces of the bones which move upon 
one another are covered with cartilage, and are contained in a 




Fig. 62. 

A section of the hip-joint taken throusrh the acetabulum and the middle of the head 
and neck of the thigh-bone. — L. T, Ligamentum teres, or round ligament, 



sort of sac, Avhich lines these cartilages and the side walls of 
the joint; and which, secreting a viscid lubricating fluid — the 
synovia — is called a synovial membrane. 



MECHANISM OF BODILY MOVEMENT. 161 

The opposed surfaces of the articular cartilages are sphe- 
roidal, cylindrical, or pulley-shaped ; and the convexities of the 
one answer, more or less completely, to the concavities of the 
other. 

Sometimes, the two articular cartilages do not come di- 
rectly into contact, but are separated by independent plates of 
cartilage, which are termed inter -articular. The opposite faces 
of these inter-articular cartilages are fitted to receive the faces 
of the proper articular cartilages. 

While these coadapted surfaces and synovial membranes 
provide for the free mobility of the bones entering into a joint, 
the nature and extent of their motion is defined, partly, by the 
forms of the articular surfaces, and, partly, by the disposition 
of the ligaments or firm fibrous cords which pass from one 
bone to the other. 

215. Ball-and-Sock9t Joints. — As respects the nature of 
the articular surfaces, joints may be what are called ball-and- 
socket joints, when the spheroidal surface furnished by one bone 
plays in a cup furnished by another. In this case the motion 
of the former bone may take place in any direction, but the 
extent of the motion depends upon the shape of the cup — 
being very great when the cup is shallow, and small in propor- 
tion as it is deep. The shoulder is an example of a ball and 
socket joint with a shallow cup ; the hip of such a joint with 
a deep cup (Fig. 62). 

216. Hinge-Joints are single or double. In the former 
case, the nearly cylindrical head of one bone fits into a corre- 
sponding socket of the other. In this form of hinge-joint the 
only motion possible is in the direction of a plane perpendicu- 
lar to the long axis of the cylinder, just as a door can only be 
made to move round an axis passing through its hinges. The 
elbow is the best example of this joint in the human body (Fig. 
63). The knee and ankle present less perfect specimens oi^ it. 

A double hhige-joint is one in which the articular surfaces 
of each bone are concave in one direction, and convex in 
another, at right angles to the former. A man seated in a 



162 



ELEMENTARY PHYSIOLOGY. 



saddle is "articulated" with the saddle by such a joint. For 
the saddle is concave from before backward and convex from 
side to side, while the man presents to it the concavity of his 



JBC— 




Fig. 63. 

Longitudinal and vertical section through the elbow-joint.— 5! Humerus; Til. ulna; 
Tr. the triceps muscle which extends the arm ; Bi. the biceps muscle which 
flexes it. 



legs astride, from side to side, and the convexity of his seat, 
from before backward. 

The metacarpal bone of the thumb is articulated with the 
bone of the wrist, called trapezium, by a double hinge-joint. 

217. A Pivot- Joint is one in which a given bone furnishes 
an axis, or pivot, on which another turns ; or itself turns on its 
own axis, resting on another bone. A remarkable example of 
the former arrangement is afforded by the atlas and axis, or 
two uppermost vertebrae of the neck (Figs. 64, 65). The axis 
possesses a vertical peg, the so-called odontoid process (6), 
and at the base of the peg are two, obliquely-placed, articular 



MECHANISM OF BODILY MOVEMENT. 



1G3 



surfaces (a). The atlas is a ring-like bone, with a massive 
thickening on each side. The inner side of the front of the 
ring plays round the neck of the odontoid peg, and the under 
surfaces of the lateral masses glide over the articular faces on 
each side of its base. A strong ligament passes between the 
inner sides of the two lateral masses of the atlas, and keeps the 
hinder side of the neck of the odontoid peg in its place (Fig. 
64). By this arrangement, the atlas is enabled to rotate 
through a considerable angle either way upon the axis, without 
any danger of falling forward or backward — accidents which 
would immediately destroy life by crushing the spinal marrow. 
The lateral masses of the atlas have, on their upper faces, 
concavities (Fig. 64, a) into which the two, convex, occipital 




Fig. 64. 



Fig. 65. 



Fig. 64. — The atlas viewed from above ; a or, upper articular surface of its lateral mass 
for the condyles of the skull: 5, the peg of the axis vertebra. 

Fig. 65.— Side view of the axis vertebra; a, articular surface for the lateral mass of 
the atlas ; &, peg or odontoid process. 

condyles of the skull fit, and in which they play upward and 
downward. Thus the nodding of the head is effected by the 
movement of the skull upon the atlas, wdiile, in turning the 
head from side to side, the skull does not move upon the atlas, 
but the atlas slides round the odontoid peg of the axis ver- 
tebra. 

The second kind of pivot-joint is seen in the forearm. If 
the elbow and forearm, as far as the wrist, are rested upon a 
table, and the elbow^ is kept firmly fixed, the hand enn never- 
theless be freely rotated so that either the palm, or the back, 
is turned directly upward. AAHien the palm is turned upward, 



IGJr 



ELEMENTARY PnYSIOLOGY. 



the attitude is cnWed supination (Fig. 66); when the back, 
pronation (Fig. 67). 

218. The Radius and TJlna. — The forearm is composed of 
two bones ; one, the ulna, which articulates with the humerus 
at the elbow by the hinge-joint ah*eady described, in such a 
manner that it can move only in flexion and extension, and has 
no power of rotation. Hence, when the elbow and wrist arc 
rested on a table, this bone remains unmoved. 

But the other bone of the forearm, the radius, has its small 
upper end, shaped like a veiy shallow cup with thick edges. 




Fig. 66.— The bores of the riVht forearm in snpinotion, 
Fig. 67— in pronation.—//, humerus; B. radius; V. ulna. 

The hollow of the cup articulates whh a spheroidal surface fur- 
nished by the humerus; the lip of the cup, with a concave de- 
pression on the side of the ulna. 

The large lower end of the radius bears the hand, and has, 



MECHANISM OF BODILY MOVEMENT. 1G5 

toward the ulna, a concave surface which articulates with the 
convex side of the small lower end of that bone. 

Thus the upper end of the radius turns as a pivot on the 
double surface, furnished to it by the ball of the humerus, and 
the partial cup of the ulna ; while the lower end of the radius 
can rotate round the pivot furnished to it by the lower end of the 
ulna. In supination^ the radius lies parallel with the ulna, with 
its lower end to the outer side of the ulna (Fig. QQ), In 
pronation^ it is made to turn on its own axis above, and round 
the ulna belov/, until its lower moiety crosses the ulna, and its 
lower end lies on the inner side of the ulna (Fig. 67). 

219. The Ligaments which keep the mobile surfaces of 
bones together are, in the case of ball-and-socket joints, strono* 
fibrous capsules which surround the joint on all sides. In hinge 
joints, on the other hand, the ligamentous tissue is chiefly ac- 
cumulated on those aspects of the joint on which motion does 
not take place, as lateral ligaments. In some cases ligaments 
are placed within the joints, as in the knee, where the bundles 
of fibres which cross obliquely between the femur and the tibia 
are called crucial ligaments ; or, as in the hip, where the round 
ligament passes from the bottom of the acr:tabulum to the ball 
furnished by the head of the femur (Fig. G2). 

Again, two ligaments pass from the apex of the odontoid 
peg to either side of the margins of the occipital foramen ; 
these, from their function in helping to stop excessive rotation 
of the skull, are called check ligaments (Fig. QS^ a). 

In one joint of the body, the hip, the socket or acetabulum 
(Fig. 62) fits so closely to the head of the femur, and the cap- 
sular ligament so completely closes its cavity on all sides, that 
the pressure of air must be reckoned among the causes which 
prevent dislocation. This has been proved experimentallv bv 
boring a hole through the floor of the acetabulum, so as to ad- 
mit air into its cavity, when the thigh-bone at once falls as far 
as the round and capsular ligaments will permit it to do, show- 
ing that it was previously pushed close up by the pressure of 
the external air. 



166 



ELEMENTARY PHYSIOLOGY. 



220. Various Kinds of Movements of Joints. — The difier- 
ent kinds of movement of which the levers thus connected are 
capable are csWed flexion and extension ; abduction and adduc- 
tion ; rotation and circumduction. 




Fig. 6S. 

The vertebral column in the upper part of the neck laid open, to show— n, the check 
ligament of the axis ; b, the broad ligament which extends from the front margia 
of the occipital foramen along the hinder faces of the bodies of the vertebra?; it 
is cut through, and the cut ends turned back to show, c, the special ligament 
which connects the point of the ""odontoid'" peg with the front margia of the 
occipital foramen ; /. the Atlas ; //. the axis. 



A limb is flexed, when it is bent; extended, when it is 
straightened out. It is abducted^ when it is drawn away from 
the middle line; adducted, when it is brought to it. It is 
rotated, when it is made to turn on its own axis ; circumducted, 
when it is made to describe a conical surface by rotation round 
an imaginary axis. 

No part of the body is capable of perfect rotation like a 
wheel, for the simple reason that such motion would neces- 
sarily tear all the vessels, nerves, muscles, etc., which unite it 
with other parts. 

221. Means of affecting them. — Given two bones united 
by a joint, and they may be moved one upon another in, at 
fewest two, different directions. In the case of a pure hinge- 
joint their directions must be opposite and in the same plane ; 



MECHANISM OF BODILY MOVEMENT. 167 

but, in all other joints, they may be in several directions and 
various planes. 

In the case of a pure hinge-joint the two practicable move- 
ments will be effected by attaching muscles to the bones on 
opposite sides of the joint (^. e., on the side toward which 
one of the bones moves when the joint is bent, and on the side 
from which it moves). When either of these muscles con- 
tracts, it will pull its attached ends together and bend the joint 
toward the side on which it is placed. 

In the other extreme form of articulation — the ball-and- 
socket joint — movement in any number of planes may be ef- 
fected, by attaching muscles in corresponding number and 
direction, on the one hand, to the bone which affords the 
socket, and on the other to that which furnishes the head. 
Circumduction will be effected by the combined and successive 
contraction of such muscles. 

222. Tendons and their Functions. — It usually happens 
that the part to which one end of a muscle is attached is ab- 
solutely or relatively fixed, while that to which the other is 
fixed is movable. In this case the attachment to the fixed 
bone is termed the origin^ that to the movable bone the inser- 
tion of the muscle. 

The fibres of muscles are sometimes fixed directly into the 
parts which serve as their origins and insertions ; but, more 
commonly, strong cords or bands of fibrous tissue, called ten- 
dons^ are interposed between the muscle proper and its place 
of origin or insertion. When the tendons play over hard sur- 
faces it is usual for them to be separated from these surfaces 
by sacs containing fluid, which are called hursce ; or even to 
be invested by synovial sheaths. 

Usually, the direction of the axis of a muscle is that of a 
straight line joining its origin and its insertion. But in some 
muscles, as the superior oblique muscle of the eye, the tendon 
passes over a pulley formed by a ligament, and completely 
alters its direction before reaching its insertion (Figs. S(S and 
87). 



168 



ELEMENTARY PHYSIOLOGY. 



Again, there are muscles which are fleshy at each end, 
and have a tendon in the middle. Such muscles are called 
digastric, or two-bellied. In the curious muscle which de- 
presses the lower jaw, and specially receives this name of di- 
gastric, the middle tendon runs through a pulley connected 
with the hyoid bone; and the muscle, which passes downward 
and forward from the skull to this pulley, after traversino* it, 
runs upward and forward, to the lower jaw (Fig. 69). 




Fig. 69. 

The course of the digastric inu«cle.— />, its posterior belly: i)^ its anterior belly; 
between the two is the tendon passing through its pulley connected with IJy. the 
hyoid bone. 



Section III. — Movements of Locomotion, 

223. Walking, — We may now pass from the consideration 
of the mechanism of mere motion to that of locomotion. 

When a man who is standing erect on both feet proceeds 
to walk, beginning with the right leg, the body is inclined so 
as to throw the centre of gravity forward ; and, the right foot 
being raised, the right leg is advanced for the length of a step, 
and the foot is put down again. In the mean while, the left 
heel is raised, but the toes of the left foot have not left the 
ground when the right foot has reached it, so that there is no 
moment when both feet are off the ground. For an instant, 
the legs form two sides of an equilateral triangle, and the cen- 
tre of the body is consequently lower than it was when the 
legs were parallel and close together. 



MOVEMENTS OF LOCOMOTION. 169 

The left foot, however, has not been merely dragged away 
from its first position, but the muscles of the calf, having come 
into play, act upon the foot as a lever of the second order, and 
thrust the body, the weight of which rests largely on the left 
astragalus, upward, forward, and to the right side. The mo- 
mentum thus communicated to the body causes it, with the 
whole right leg, to describe an arc over the right astragalus, on 
which that leg rests below. The centre of the body conse- 
quently rises to its former height as the right leg becomes ver- 
tical, and descends again as the right leg, in its turn, inclines 
forward. 

When the left foot has left the ground the body is supported 
on the right leg, and is well in advance of the left foot ; so that, 
without any further muscular exertion, the left foot swings for- 
ward like a pendulum, and is carried, by its own momentum, 
beyond the right foot, to the position in which it completes the 
second step. 

224. Economy of Force in Walking. — When the inter- 
vals of the steps are so timed that each swinging leg comes for- 
ward into position for a new step, without any exertion on the 
part of the walker, walking is effected with the greatest possible 
economy of force. And as the swinging leg is a true pendu- 
lum, the time of vibration of which depends, other things being 
alike, upon its length (short pendulums vibrating more quickly 
than long ones), it follows that, on the average, the natural 
step of short-legged people is quicker than that of long-legged 
ones. 

225. Ennning and Jumping.— In running there is a pe- 
riod when both legs are off the ground. Tlie legs are ad- 
vanced by muscular contraction, and the lever action of each 
foot is swift and violent. Indeed, the action of each leg resem- 
bles, in violent running, that which, when both legs act to- 
gether, constitutes a jump, the sudden extension of the legs 
adding to the impetus, which, in slow walking, is given only 
by the feet. 



170 ELEMENTAEY PHYSIOLOGY. 



Section IV. — Vocal Movements. 

226. Conditions of the Production of Voice.— Perhaps 

the most singular motor apparatus in the body is the larynXy 
by the agency of which voice is produced. 




Fig. to. 

Diagram of the larynx, the thyroid cartilage being supposed to be transparent, and 
allowing the right arytenoid cartilage (^r.), vocal ligament (F.), and thyro-aryte- 
noid muscle {th.A.^, the upper part of the cricoid cartilage (O'.), and the attach- 
ment of the epiglottis {Ep.), to be seen ; C.th, the right crico-thyroid muscle ; TV. 
the trachea ; Ily. the hyoid bone. 

The essential conditions of the production of the human 
voice are : 

a. The existence of the so-called vocal chords. 

b. The parallelism of the edges of these chords, without 
which they will not vibrate in such a manner as to give out 
sound. 

c. A certain degree of tightness of the vocal chords, without 
which they will not vibrate quickly enough to produce sound. 

d. The passage of a current of air between the parallel 
edges of the vocal chords sufficiently powerful to set the chords 
vibrating. 

227. The Vocal Chords. — The vocal chords are, properly 
speaking, not " chords " at all, but elastic cushions with broad 



VOCAL MOVEMENTS. 



171 



bases, fixed to the larynx, and sharp free edges, whicli consti- 
tute the lateral boundaries of the glottis. In front, the ends 
of the edges of these vocal cushions are attached, close to- 




FiG. 71. 

A vertical and transverse section througrh the larynx, the hinder half of which is re- 
moved.—^. Epiglottis; 77i. thyroid cartilage; a, cavities called the 'centricles 
of the larynx above the vocal ligaments ( F) ; x the right thyro -arytenoid mus- 
cle cut across ; Cr, the cricoid cartilage. 



gether, to the reentering angle of the thyroid cartilage ; be- 
hind, to the arytenoid cartilages. These, when left to them- 
selves, diverge, so that, in the quiescent state, the aperture of 
the glottis is V-shaped, the point of the V. being forward and 
the base behind (Fig. 72). Under these circumstances a cur- 
rent of air passing through the glottis produces no sound ; 
whence it is that ordinary expiration and inspiration take place 
quietly. 

228. The Cartilages of the Larynx. — The thyroid car- 
tilage is a broad plate of gristle bent upon itself so as to have a 
V shape, and so disposed that the point of the V is turned for- 
ward, and constitutes what is commonly called " Adam's apple." 
Above, the thyroid cartilage is attached to the hyoid bone. 



172 



ELEMENTARY PHYSIOLOGY, 



Below and 1)ehincl, its broad sides are produced into little 
elongations or horns, which are connected by ligaments with 
the outside of a great ring of cartilage, the cricoid^ which forms, 
as it were, the top of the windpipe. The cricoid ring is much 
higher behind than in front, and a gap, filled up only by mem- 
brane, is left between its upper edge and the lower edge of the 
front part of the thyroid, when the latter is horizontal. Con- 
sequent! 3% the thyroid cartilage can be moved up and down 
through the space left by this membrane, turning upon the 
articulation of its horns with the hinder part of the cricoid, as 
upon hinges. When it moves downward, the distance between 
the front part of the thyroid cartilage and the back of the cri- 
coid is necessarily increased ; and when it moves back again to 
the horizontal position, diminished. There is, on each side, a 
large muscle, the crico-ihyroid, which passes from the outer 
side of the cricoid cartilage obliquely upward and backward to 
the thyroid, and pulls the latter down (Fig. 70). 




^7^/i. 



Fig. 72. 
The parts surrounding the glottis partially dissected and viewed from above. — 77i. 
The thyroid cartilage; Cr. the cricoid cartilage; V, the edges of the vocal liga- 
ments bounding the glottis; Ari/. the arytenoid cartilage; Th.A. thyro-aryte- 
noid ; r.a.Z. lateral crico-arytenoid; Ca.p. posterior crico-arytenoid; -4r.jp. pos- 
terior arytenoid muscles. 

229. The Muscles of the Larynx. — The two arytenoid 
cartilages are perched side by side upon the upper edge of the 



VOCAL MOVEMENTS. 



173 



back part of the cricoid, and are freely articulated therewith. 
Muscles are so disposed as to pull them toward, or away from, 
one another ; and a pair of strong muscles which proceed from 
their bases to the reentering angle of the thyroid alongside the 
vocal chords, and are called thijro-arytenoid^ tend to pull the 
thyroid cartilage up when it has been depressed by the crico- 
thyroid muscles. 

When the muscles called posterior arytenoid^ which, pass- 
ing between the two arytenoid cartilages, cause them to ap- 
proach one another, contract, they bring the hinder ends of the 
vocal chords together, and make their edges parallel. The 
expiratory muscles now force air from the chest through the 
larynx, and a musical note, the voice, is produced. 




Fig. 73. 

DiaETi'am of a model ilinstrating the action of the levers and mnsclos of the larynx. 
The stand and vertical pillar repres'^nt the cricoid and arytenoid cartilaires, while 
the rod {h c), moving on a pivot at c, takes the place o\ the thyroid cartilage ; a b 
is an elastic band representing the vocal ligament. Parallel with this runs a cord 
fastened at one end to b c, and at the other, passing over a pulley to the weight 
B. This represents the thyro-arytenoid muscle. A cord attached to the middle 
of h c, and passing over a second pulley to the weight A, represents the crico- 
thyroid muscle, it is obvious that when the bar {b c) is pulled down to the posi- 
tion c c/, the elastic band (a b) is put on the stretch. 

230. Notes— Range and Quality of Voice.— Other things 
being alike, the musical note will be low or high, according as 
the vocal chords are relaxed or tightened ; and this again de- 
pends upon the relative predominance of the contraction o( the 
crico-thyroid and tliyro-arytenoid muscles: for when the thyro- 
arytenoid muscles are fully contracted, the thyroid cartilage 



174 ELEMENTARY PHYSIOLOGY. 

will be pulled up as far as it can go, and the vocal chords will 
be as lax as they can be ; while, when the crico-thyroid mus- 
cles are fully contracted, the thyroid cartilage will be pulled 
down as far as it can go, and the vocal chords will be stretched 
as far as possible. 

The range of any voice depends upon the difference of ten- 
sion which can be given to the vocal chords, in these two posi- 
tions of the thyroid cartilage. Accuracy of singing depends 
upon the precision with which the singer can voluntarily adjust 
the contractions of the thyro-arytenoid and crico-thyroid mus- 
cles — so as to give his vocal chords the exact tension at which 
their vibration will yield the notes required. 

The quality of a voice — treble, base, tenor, etc., on the 
other hand, depends upon the make of the particular larynx, 
the primitive length of its vocal chords, their elasticity, the 
amount of resonance of the surrounding parts, and so on. 

Thus, men have deeper notes than boys and women, be- 
cause their larynges are larger and their vocal chords longer — 
whence, though equally elastic, they vibrate less swiftly. 

231. Speech— Vowel and Consonant Sounds. — Speech is 
voice modulated by the throat, tongue, and lips. Thus voice 
may exist without speech ; and it is commonly said that speech 
may exist without voice, as in whispering. This is only true, 
however, if the title of voice be restricted to the sound pro- 
duced by the vibration of the vocal chords ; for, in whispering, 
there is a sort of voice produced by the vibration of the mus- 
cular walls of the lips, which thus replace the vocal chords. A 
whisper is, in fact, a very low whistle. 

The modulation of the voice into speech is effected by 
changing the form of the cavity of the mouth and nose, by the 
action of the muscles which move the walls of those parts. 

Thus, if the pure voiuel sounds 

E (as in Ac), A (as in hay)^ A' (as in ah\ 

(as in or), 0' (as in oA), 00 (as in cool), 

are pronounced successively, it will be found that they may be 
all formed out of one note, produced by a continuous expira- 



VOCAL MOVEMENTS. 175 

tion, the mouth being kept open, but the form of its aperture 
being changed for each vowel. It will be narrowest, with the 
lips most drawn back, in E^ widest in A\ and roundest, with 
the Ups most protruded, in 00, 

Certain consonants also may be pronounced without inter- 
rupting the current of the expired air, by modification of the 
form of the throat and mouth. 

Thus the aspirate, H, is the result of a little extra expira- 
tory force — a sort of incipient cough. S and Z, Sh and e/(as 
in jugular =G soft, as in gentry)^ Th^ Z, R^ F, F, may like- 
wise all be produced by continuous currents of air forced 
through the mouth, the shape of the cavity of which is pecu- 
liarly modified by the tongue and lips, 

232. Blocking the Air-Current. — All the vocal sounds 
hitherto noted so far resemble one another, that their produc- 
tion does not involve the stoppage of the current of air which 
traverses either of the modulating passages. 

But the sounds of If and iV^can only be formed by blocking 
the current of air which passes through the mouth, while free 
passage is left through the nose. For M, the mouth is shut by 
the lips; foriV, by the application of the tongue to the palate. 

233. Explosive Consonants. — The other consonantal 
sounds of the English language are produced by shutting the 
passage through both nose and mouth; and, as it were, for- 
cing the expiratory vocal current through the obstacle furnished 
by the latter, the character of which obstacle gives each con- 
sonant its peculiarity. Thus, in producing the consonants B 
and P the mouth is shut by the lips, which are then forced 
open in this explosive manner. In T and D the mouth pas- 
sage is suddenly barred by the application of the point of the 
tongue to the teeth, or to the front part of the palate ; while 
in K and G (hard, as in go) the middle and back of the tongue 
are simihu-ly forced against the back part of the palate. 

234. Speaking - Machines. — An artificial larynx may be 
made by the proper adjustment of elastic bands, which take the 
place of the vocal chords ; and when a current of air is forced 



176 ELEMENTARY PHYSIOLOGY. 

through these, due regulation of the tension of the bands will 
give rise to all the notes of the human voice. As each vowel 
and consonantal sound is produced by the modification of the 
form of the cavities, which lie over the natural larynx ; so, by 
placing over the artificial larynx chambers to which any requi- 
site shape can be given, the various letters may be sounded. 
It is by attending to these facts and principles that various 
speaking-machines have been constructed. 

235. Tongueless Speech. — Although the tongue is credited 
with the responsibility of speech, as the "unruly member," 
and undoubtedly takes a very important share in its produc- 
tion, it is not absolutely indi^ensable. Hence, the apparently 
fabulous stories of people who have been enabled to speak after 
their tongues had been cut out by the cruelty of a tyrant or 
persecutor, may be quite true. 

Some years ago I had the opportunity of examining a per- 
son, whom I will call Mr. E., whose tongue had been removed 
as completely as a skilful surgeon could perform the operation. 
"When the mouth was widely opened, the truncated face of the 
stump of the tongue, apparently covered with new mucous 
membrane, was to be seen, occupying a position as far back as 
the level of the anterior pillars of the fauces. The dorsum of 
the tongue was visible with difiiculty ; but I believe I could dis- 
cern some of the circum vallate papillae upon it. 'Nona of these 
were visible upon the amputated part of the tongue, which had 
been preserved in spirit; and which, so far as I could judge, 
was about 2-| inches long. 

When his mouth was open, Mr. E. could advance his 
tongue no farther than the position in which I saw it ; but he 
inforaied me that when his mouth was shut, the stump of the 
toufyue could be brouo-ht much more forward. 

Mr. E.'s conversation was perfectly intelligible ; and such 
words as think, the, coiv, kill, were well and clearly pro- 
nounced. But tin became fin y tack, fack or pack ; toll, ^00/ ; 
dog, ihop ; dine, vine; dew, thew ; cat, catf ; mad, madf ; 
goose, gooth : big, pig, hich, jnch, with a guttural ch. 



VOCAL MOVEMENTS. 177 

In fact, only tlie pronunciation of those letters the forma- 
tion of which requires the use of the tongue was afiected ; and, 
of these, only the two which involve the employment of its 
tip, were absolutely beyond Mr. E.'s power. He converted all 
fs and d^s into /'5, p'^, v^s, or th''s, Th was fairly given in all 
cases ; s and sA, I and r, with more or less of a lisp. Initial 
g's and F5 were good ; but final g^8 were all more or less gut- 
tural. In the former case, the imperfect stoppage of a current 
of air by the root of the tongue was of no moment, as the 
sound ran on into that of the following vowel ; while, Avheu 
the letter was terminal, the defect at once became obvious. 



CHAPTER IX. 

OF SENSATIONS AND SENSORY ORGANS. 

Section I. — Reflex Action — Groups of Sensations. 

236. Efferent and Afferent Nerves. — ITie agent by which 
all the motor organs (except the cilia) described in the pre- 
ceding chapter are set at work is muscular fibre. But, in the 
living body, muscular fibre is made to contract only by a 
change which takes place in the motor or efferent nerve, which 
is distributed to it. This change again is effected only by the 
activity of the central nervous organ, with which the motor 
nerve is connected. The central organ is thrown into activity 
immediately or ultimately, only by the influence of changes 
which take place in the molecular condition of nerves, called 
sensor7j or afferent, which are connected, on the one hand, with 
the central organ, and, on the other hand, wdtli some other 
part of the body. Finally, the alteration of the afferent nerve 
is itself produced only by changes in the condition of the part 
of the body with which it is connected, and whieh usually re- 
sult from external impressions. 
8* 



178 ELEMENTARY PHYSIOLOGY. 

237. Conveyance of Molecular Impressions. — Thus the 
great majority (if not the Avhole) of the movements of the body 
and of its parts are the effect of an influence (technically 
termed a stimulus or irritation) applied directly, or indirectly, 
to the ends of afferent nerves, and giving rise to a molecular 
change, which is propagated along their substance to the 
central nervous organ with which they are connected. The 
molecular activity of the afferent nerve communicates itself to 
the central organ, and is then transmitted along the motor 
nerves, which pass from the central organ to the muscles 
affected. And when the disturbance in the molecular condi- 
tion of the efferent nerves reaches their extremities, it is com- 
municated to the muscular fibres, and causes their particles to 
take up a new position, so that each fibre shortens and be- 
comes thicker. 

238. Eeflex Action. Sensations and Consciousness. — 
Such a series of molecular changes as that just described is 
called a reflex action — the disturbance caused by the irritation 
being as it were reflected back, along the motor nerves, to the 
muscles. 

A reflex action, strictly so called, takes place without our 
knowing any thing about it, and hundreds of such actions are 
going on continually in our bodies without our being aware of 
them. But it very frequently happens that we learn that 
something is going on, when a stimulus affects our afl'erent 
nerves, by having w-hat we call a feeling or sensation. We 
class sensations along with emotions^ and volitions, and thoughts, 
under the common head of states of consciousness. But what 
consciousness is, we know not; and how it is that any thing so 
remarkable as a state of consciousness comes about as the re- 
sult of irritating nervous tissue, is just as unaccountable as the 
appearance of the Djin when Aladdin rubbed his lamp in the 
story, or as any other ultimate fact of nature. 

239. Subjective Sensations. — Sensations are of very vari- 
ous degrees of definiteness. Some arise within ourselves, we 
know not how^ or where, and remain vague and undefinable. 



KEFLEX ACTION — GROUPS OF SENSATIONS. 179 

Such are the sensations of uncomfortableness^ of faintness^ of 
fatigue^ or of restlessness. We cannot assign any particular place 
to these sensations, which are very probably the result of affec- 
tions of the afferent nerves in general, by the state of the blood, 
or that of the tissues in which they are distributed. And how- 
ever real these sensations may be, and however largely they 
enter into the sum of our pleasures and pains, they tell us ab- 
solutely nothing of the external world. They are not only 
diffuse, but they are subjective sensations. 

240. The Muscular Sense. — What is termed the muscular 
sense is less vaguely localized than the preceding, though its 
place is still incapable of being very accurately defined. This 
muscular sensation is the feeling of resistance which arises 
when any kind of obstacle is opposed to the movement of the 
body, or of any part of it; and it is something quite different 
from the feeling of contact, or even of pressure. 

Lay one hand flat on its back upon a table, and rest a disk 
of cardboard a couple of inches in diameter upon the ends of 
the outstretched fingers ; the only result will be a sensation of 
contact — the pressure of so light a body being inappreciable. 
But put a two-pound weight upon the cardboard and the sen- 
sation of contact will be accompanied, or even obscured, by 
the very different feeling of pressure. Up to this moment the 
fingers and arm have rested upon the table; but now let the 
hand be raised from the table, and another new feeling will 
make its appearance — that of resistance to effort. This feeling 
comes into existence with the exertion of the muscles w^hich 
raise the arm, and is the consciousness of that exertion given 
to us by the muscular sense. 

Any one who raises or carries a weight knows w^U enough 
that he has this sensation ; but he may be greatly puzzled to 
say where he has it. Nevertheless, the sense itself is very deli- 
cate, and enables us to form tolerably accurate judgments of 
the relative intensity of resistances. Persons w^ho deal in arti- 
cles sold by weight are constantly enabled to form very precise 
estimates of the weight of such articles by bwalancing them in 



180 ELEMENTARY PHYSIOLOGY. 

their hands; and, in this case, they depend in gi'cat measure 
upon the muscular sense. 

241. The Higher Senses. — In a third group of sensations, 
each feeling, as it arises, is assigned to a definite part of the 
body, and is produced by a stimulus applied to that part of the 
body ; but the bodies, or forces, which are competent to act as 
stimuli, are very various in character. Such are the sensations 
of touchy taste^ and smell, which are restricted to the membranes 
which cover the surface of the body and line the mouth and 
nasal cavities. 

And lastly, in a fourth group of sensations, each feeling 
requires for its production the application of a single kind of 
stimulus to a very specially modified part of the integument. 
The latter serves as an intermediator between the physical 
agent of the sensation and the sensory nerve, which is to con- 
vey to the brain the impulse necessary to awake that stat^ of 
consciousness, which we call the sensation, in it. Such are the 
sensations of sight and hearing. The physical agents which 
can alone awaken these sensations (under natural circumstances) 
are light and sound. The modified parts of the integument, 
which alone are competent to intermediate between these agents 
and the nerves of sight and hearing, are the ei/e and the ear. 

2i2. General Plan of a Sensory Organ. — In every sensory 
organ it is necessary to distinguish the terminal expansion of 
the afi'erent or sensory nerve, and the structures which inter- 
mediate between this expansion and the physical agent which 
gives rise to the sensation. 

And in each group of special sensations there arc certain 
phenomena which arise out of the structure of the organ, and 
others which result from the operation of the central apparatus 
of the nervous system upon the materials supplied to it by the 
sensory organ. 

Section II. — Touchy Taste, and Smell, 

243. The Sense of Touch. — The sense of Touch (including 
that of heat and cold) is possessed, more or less acutely, by all 



TOUCH, TASTE, AND SMELL. 181 

parts of the free surface of the body, and by tbe walls of the 
moutli and nasal passages. 

Whatever part possesses this sense consists of a membrane 
(integumentary or mucous) composed of a deep layer made up 
of fibrous tissue, containing a capillary net-work and the ulti- 
mate terminations of the sensory nerves ; and of a supei-ficial 
layer consisting of epithelial or epidermic cells, among which 
are neither nerves nor vessels. 

Wherever the sense of touch is delicate, the deep layer is 
not a mere flat expansion, but is raised up into multitudes of 
small, close-set, conical elevations, which are called papillce. 
In the sldn, the coat of epitheUal or epidermic cells does not 
follow the contour of these papillse, but dips down between 
them and forms a tolerably even coat over them. Thus, the 
points of the papillse are much nearer the surface than the 
general plane of the deep layer whence these papillse proceed. 

Loops of vessels enter the papillse, and the fine ultimate 
terminations of the sensory nerve fibres distributed to the sldn 
terminate in them, but in what way has not been thoroughly 
made out. 

In certain cases, the delicate fibrous sheath, or neurilemma^ 
of the nerve which enters the papilla, enlarges in the papilla 
into an oval swelling, which is called a tactile corpuscle. These 
corpuscles are only found in the papillse of those localities which 
are endowed with a very delicate sense of touch, as in the tips 
of the fingers, the point of the tongue, etc. 

244. Functions of Epithelium. — It is obvious from what 
has been said that no direct contact takes place between a 
body which is touched and the sensory nerve, a thicker or 
thinner layer of epithelium, or epidermis, being situated be- 
tween the two. In fact, if this layer is removed, as when a 
surface of the skin has been blistered, contact with the raw 
surfiicc gives rise to a sense of pain, not to one of touch prop- 
erly so called. Thus, in touch, it is the epidermis, or epithe- 
lium, which is the intermediator between the nerve and the 
physical agent, the external pressure being transmitted through 



182 ELEMENTARY PHYSIOLOGY. 

the horny cells to the subjacent ends of the nerves, and the 
kind of impulse thus transmitted must be modified by the 
thickness and character of the cellular layer, no less than by 
the forms and number of the papillae. 

245. Varying Tactile Sensibility. — Certain very curious 
phenomena appertaining to the sense of touch are probably 
due to these varying anatomical arrangements. Not only is 
tactile sensibility to a single impression much duller in some 
parts than in others — a circumstance which might be readily 
accounted for by the different thickness of the cellular layer — 
but the power of distinguishing double simultaneous impres- 
sions is very different. Thus if the ends of a pair of com- 
passes (better if blunted with pointed pieces of cork) are sep- 
arated by only one-tenth or one-twelfth of an inch, they will 
be distinctly felt as two, if applied to the tips of the fingers ; 
whereas if applied to the back of the hand in the same way, 
only one impression will be felt ; and, on the arm they may be 
separated for a quarter of an inch, and still only one impres- 
sion will be perceived. 

Accurate experiments have been made in different parts of 
the body, and it has been found that two points can be dis- 
tinguished by the tongue, if only one-twenty-fourth of an inch 
apart; by the tips of the fingers if one-twelfth of an inch dis- 
tant; while they may be one inch distant on the cheek, and 
even three inches on the back, and still give rise to only one 
sensation. 

246. The Sense of Warmth or Cold.— The feeling of 
warmth, or cold, is the result of an excitation of sensory 
nerves distributed to the skin, which are probably distinct 
from those which give rise to the sense of touch. And it 
would appear that the heat must be transmitted through the 
cellular layer to give rise to this sensation ; for just as touch- 
ing a naked nerve, or the trunk of a nerve, gives rise only to 
pain, so heating or cooling an exposed nerve, or the trunk of a 
nerve, gives rise not to a sensation of heat or cold, but simply 
to pain. 



TOUCH, TASTE, AND SMELL. 183 

Again, the sensation of heat, or cold, is relative rather than 
absolute. Suppose three basins be. prepared, one filled ^vith 
ice-cold water, one with water as hot as can be borne, and the 
third with a mixture of the two. If the hand be put into the 
hot-water basin, and then transferred to the mixture, the latter 
will feel cold ; but if the hand be kept awhile in the ice-cold 
water, and then transferred to the very same mixture, it will 
feel warm. 

Like the sense of touch, the sense of warmth varies in deli- 
cacy in different parts of the body. 

The cheeks are very sensitive, more so than the lips ; the 
palms of the hands are more sensitive to heat than their backs. 
Hence a washerwoman holds her flat-iron to her cheek to test 
the temperature, and one who is cold spreads the palms of his 
hands to the fire. 

247. The Sense of Taste— the Tongue. —The organ of 
the sense of Taste is the mucous membrane which covers the 
tongue, especially its back part and the hinder part of the 
palate. Like that of the skin, the deep, or vascular, layer of 
the mucous membrane of the tongue is raised up into papillae, 
but these are large, separate, and have separate coats of epi- 
thelium. Toward the tip of the tongue they are for the most 
part elongated and pointed, and are called filiform ; over the 
rest of the surface of the tongue, these are mixed with other, 
larger, papilla) with broad ends and narrow bases, called /^m^/- 
form ; but toward its root there are a number of large papil- 
lae, set in the shape of a V with its point backward, each of 
which is like a fungiform papilla surrounded by a wall. These 
arc the circumvallate papillae (Fig. 74, C.p,), The larger of 
these papillae have subordinate small ones upon their surfoces. 
They are very vascular, and they receive nervous filaments 
from two sources, the one the nerve called glossophan/nacaJ, 
the other the fifth nerve. The latter chiefly supplies the front 
of the tongue, the former its back and the adjacent part of the 
palate ; and there is reason to believe that it is the latter re- 
gion which is more especially the seat of the sense of taste. 



18i 



ELEMENTAEY PHYSIOLOGY. 



The great majority of the sensations we call taste, how- 
ever, are in reality complex sensations, into which smell and 
even touch largely enter. 




Fig. 74. 

The mouth widely opened, to show the toni^ue and palate. — Vv. the nvula; Tr. the 

tonsil between the anterior and posterior pillars of the fauces; C.p. circumval- 

lato papilhe; i^. /?. fungiform papilla-. The minute filiform papillcC cover the 

• interspaces between these. On the right side the tongue is partially dissected to 

show the course of the filaments of the glossopharyngeal nerve, VIIL 

248. Smell— Mechanism of the Nostrils. — The organ of 
the sense of Smell is the delicate mucous membrane which 
lines a part of the nasal cavities, and is distinguished from the 
rest of the mucous membrane of these cavities — firstly, by pos- 
sessing no cilia ; secondl}^ by receiving its nervous supply from 
the olfactory, or first, pair of cerebral nerves, and not, like the 
rest of the mucous membrane, from the fifth pair. 

Each nostril leads into a spacious nasal chamber, separated, 
in the middle line, from its fellow of the other side, by a parti- 



TOUCH, TASTE, AND SMELL. 



185 



tion or septum^ formed partly by cartilage and partly by bone, 
and continuous with that partition which separates the two 
nostrils one from the other. Below, each nasal chamber is 
separated from the cavity of the mouth by a floor, the bony 
palate (Figs. 75, 76, 77), and when this bony palate comes to 
an end, the partition is continued down to the root of the 
tongue by a fleshy curtain, the soft palate, which has already 
been described. The soft palate and the root of the tongue 




JPa 



Fig. 75. 



Fig. 76. 



Yertical longitudinal sections of the nasal cavity. — The left-hand figure represents 
the outer wall of the right nasal cavity; the right-hand figure the left side of the 
middle partition or septur^i of the nose, which forms the right wall cf the left 
nasal cavity. ./, the olfactory nerve and its branches; F, branches of the fifth 
nerve; Pa. the palate Avhich separates the nasal cavity from that of the mouth; 
S. T. the superior turbinal bone; M. T. the middle turbinal ; /. T. the inferior 
turbinal. The letter /is placed in the cerebral cavity, and the partition on which 
the Olfactory lobe rests, and through which the filaments of the olfactory nerves 
pass, is the cribriform plate. 

together, constitute, under ordinary circumstances, a transverse 
movable partition between the mouth and the pharynx, and it 
will be observed that the opening of the larynx, the glottis^ lies 
behind the partition ; so that while the latter is complete, no 
passage of air can take place between the mouth and the 
pharynx. But above and behind the partition are the two 
hinder openings of the nasal cavities (which are called the pos- 
terior nares) separated by the termination of the septum, and 
by means of these wide openings the air passes, with great 
readiness, from the nostrils along the lower part of each nasal 
chamber to the glottis, or in the opposite direction. It is by 
means of the passages thus freely open to the air that we breathe, 
as wc ordinarily do, Avitli the mouth shut (Fig. 53). 



186 



ELEMENTARY PHYSIOLOGY. 



Each nasal chamber rises, as a high vault, far above the 
level of the arch of the posterior nares — in fact, about as hio-h 
as the depression of the root of the nose. The uppermost and 
front part of its roof, between the eyes, is formed by a delicate 
horizontal plate of bone, perforated like a sieve by a great many 
small holes, and thence called the cribriform plate (Fig. 77). 
It is this plate alone which, in this region, separates the cavity 
of the nose from that which contains the brain. The olfactory 
lobes, which are directly connected with, and, indeed, a part 

Cn 




:^77. 



A transverse and vertical section of the nasal cavity taken nearly through the letter 
/in the foregoing figure.— 6>. the cribriform plate; S. T., 31. T. the chambered 
superior and middle turbinal bones on which and on the septum, Sp. the fila- 
ments of the olfactory nerve are distributed ; /. T. the inferior turbinal bone; PI. 
the palate ; An. the Antrum or chamber which occupies the greater part of the 
maxillary bone and opens into the nasal cavity. 

of the brain, enlarge at their ends, and their broad extremities 
rest upon the upper side of the cribriform plate, sending im- 
mense numbers of delicate filaments, the olfactory nerves, 
through it to the olfactory mucous membrane (Figs. 75, 76). 

On each wall of the septum this mucous membrane forms 
a flat expansion, but, on the side walls of each nasal cavity, it 
follows the elevations and depressions of the inner surfaces of 
what are called the upper and middle turbinal^ or spongy bones. 
These bones are called spongy, because the interior of each is 



TOUCH, TASTE, AND SMELL. 187 

occupied by air cavities separated only by very delicate parti- 
tions, and communicating with the nasal cavities. Hence the 
bones, though massive-looking, are really exceedingly light and 
delicate, and fully deserve the appellation of spongy (Fig. 77). 

There is a third light scroll-like bone distinct from these 
two, and attached to the maxillary bone, which is called the 
inferior turbinal, as it lies lower than the other two, and im- 
perfectl}^ separates the air-passages from the proper olfactory 
chamber (Fig. 77). It is covered by the ordinary ciliated 
mucous membrane of the nasal passages, and receives no fila- 
ments from the olfactory nerve (Figs. 7o, 76), 

249. The Reason of " Sniffing." — From the arrangements 
which have been described it is clear that, under ordinary cir- 
cumstances, the gentle inspiratory and expiratory currents will 
flow along the comparatively wide, direct passages afforded by 
so much of the nasal chamber as lies below the middle turbinal, 
and that they will hardly move the air enclosed in the narrow 
interspace between the septum and the upper and middle 
spongy bones, which is the proper olfactory chamber. 

If the air currents are laden with particles of odorous mat- 
ter, these particles can only reach the olfactory membrane by 
diffusing themselves into this narrow interspace ; and if there 
be but few of these particles, they will run the risk of not reach- 
ing the olfactory mucous membrane at all, unless the air in 
contact with it be exchanged for some of the odoriferous air. 
Hence it is that, when we wish to perceive a faint odor more 
distinctly, we sniff, or snufF up, the air. Each sniff is a sudden 
inspiration, the effect of which must reach the air in the olfac- 
tory chamber at the same time as, or even before, it affects that 
at the nostrils, and thus must tend to draw a little air out of 
that chamber from behind. At the same time, or immediately 
afterward, the air sucked in at the nostrils, entering with a sud- 
den vertical rush, part of it must tend to flow directly into the 
olfactory chamber, and replace that thus drawn out. 

The loss of smell which takes place in the course of a severe 
cold may, in part, be due to the swollen state of the mucous 



188 ELEMENTARY PHYSIOLOGY. 

membrane wliicb covers the inferior turbinal bones, which thus 
impedes the passage of odoriferous air to the olfactory chamber. 

Section III. — The Mechanism of Hearing, 

250. Structure of the Organ. — The essential organ of the 
sense of Hearing consists, on each side, of two parts, the mem- 
branous labyrinth, and the scala media of the cochlea^ both of 
which small organs are lodged in the midst of a dense and solid 
mass of bone (thence called ^^e^rosaZ), forming a part of the 
temporal bone, and entering into the base of the skull. 

Each of these essential constituents of the organ of hearing 
is, substantially, a membranous bag filled with a fluid, and sup- 
ported in fluid. In the interior of each, certain small, mobile, 
hard bodies are contained ; and the ultimate filaments of the 
auditory nerves are so distributed upon the walls of the bags 
that their terminations must be knocked by the vibrations of 
these small hard bodies, should any thing set them in motion. 
It is also quite possible that the vibrations of the fluid contents 
of the sacs may themselves suffice to aff*ect the filaments of the 
auditory nerve ; but, however this may be, any such efixict must 
be greatly intensified by the cooperation of the solid particles. 

In bathing in a tolerably smooth sea, on a rocky shore, the 
movement of the little waves, as they run backward and for- 
ward, is hardly felt by any one who lies down upon the beach; 
but, if the beach be sandy and gravelly, the pelting of the 
showers of little stones and sand, which are raised and let fall 
by each wavelet, makes a very definite impression on the nerves 
of the skin. 

Now the membrane on which the ends of the auditory 
nerves are spread out is virtually a sensitive beach, and waves 
which, by themselves, would not be felt may be readily per- 
ceived if they suffice to raise and let fall hard particles. 

In the membranous labyrinth these hard bodies are hair- 
like filaments, or minute particles of calcareous sand. The 
latter are called otoconia, or otolithes. 



THE MECHANISM OF HEARING. 



189 



The epithelium (a, Fig. 78) which covers the termination 
of the nerves in the ampullse (see p. 190) which is produced 
into long stiff slender hair-like processes (6, Fig. 78), which are, 
of course, readily affected by any vibration of the endolymph, 
and communicate the impulse to the end of the nerves. In 




Fig. 78. 
The delicate stiff filaments which are set upon the inner walls of the ampullae. 

the vestibular sac (p. 190), on the contrary, these hairs are 
scanty or absent, but the minute angular octoconia serve the 
same purpose. 

In the scala media of the cochlea organized structures, 
minute, rod-like bodies, having a definite form, length, and 
more or less cellular structure, the fibres of Cord, appear to 
serve the same object. 

251. The Vestibule. — For simplicity's sake, the membra- 
nous labyrinth and the scala media have hitherto been spoken 
of as if they were simple bags ; but this is not the case, each 
bag having a very curious and somewhat complicated form. 

Thus the memhranoiis labyrinth has the figure of an oval 



190 ELEMENTARY PHYSIOLOGY. 

vestibular sac, witli which the hooplike semicircular canals are 
connected. These are three in number, and two being vertical 
are called the anterior and posterior vertical semicircular canals ; 
while the third, lying outside, and horizontally, is termed the 
external^ or horizontal semicircular canal. One end of each of 
these canals is dilated into what is called the amjmlla (Figs. 
80, 82). 

It is upon the walls of these ampullae and those of the 
vestibular sac that the nerves are distributed (p. 189). 

The fluid w^hich fills the cavities of the semicircular canals 
and sac is termed endolymph. That which separates these 
delicate structures from the bony chambers in which they are 
contained is the perilymph. Each of these fluids is little more 
than water. 

252. The Cochlea. — In the scala media of the cochlea the 
primitive bag is drawn out into a long, band-like tube, which 
is coiled two and a half times on itself into a conical spiral, 
and lies in a much wider chamber of corresponding form, ex- 
cavated in the petrous bone {Coc, Fig. 80). Each edge of the 
scala media is fastened to the walls of the containing chamber, 
which thus becomes divided into tw^o passages, which com- 
municate at the summit of the spire, but are elsewhere sepa- 
rate. These two passages are called respectively the scala 
tympani and scala vestibule and are filled with perilymph. 

The fibres of the auditory nerve (vil Fig. 79) are distrib- 
uted to the whole length of the scala media. They enter it 
by the edge which is attached to the inner wall of the bony 
cochlea, formed by the central pillar or modiolus^ round which 
the cavity winds. 

That wall of the scala media [e) which separates it from the 
scala vestibuli is called the uioper membrane of Corti. The 
opposite wall, w^hich separates it from the scala tympani, is the 
basilar membrane. It is very elastic, and on it rests the fibres 
of Corti [C (7'), each of which is composed of two filaments 
joined at an angle. An immense number of these filaments 
are set side by side, with great regularity, throughout the 



THE MECHANISM OF HEARING. 



191 



whole length of the scala media, so that this presents almost 
the appearance of a keyboard, if viewed from either the scala 



iS^ca>T. 



ScaJ^ 



ScaM 




iScccJU^-ik- 



Fig. 79. 

A section through the ^cala media of the cochlea.— or, The inner wall pillar, or modi- 
olus of the bona cochlea; c, its outer wall; Sea. T. the cavity of the scala tym- 
pani ; Sea. V. the cavity of the scala vestibuli ; Sea. 3f. the cavity of the scola 
media itself; c?, the elastic hasilar membrane which separates the scala media 
itself from the scala tympani ; V. a vessel which lies in this cut through ; e. the 
so-culled upper membrane of Corti which separates the scala media from the 
scala vestibuli; C C, the fibres of Corti; VIL the filaments of the auditory nerve. 

vestibuli or the scala tympani. The ends of the nerves come 
into close relation with these fibres, which are capable of being 
agitated by the slightest impulse. 



192 



ELEMENTARY PHYSIOLOGY 



253. The Bony Labyrintli. — These essential parts of the 
organ of hearing are lodged in chambers of the petrous part 
of the temporal bone. Thus the membranous labyrinth is 
contained in a cavity of corresponding form, of which that part 
which lodges the sac is termed the vestihtde, and that which 
contains the semicircular canals, the boiij/ semicircular canals. 
Furthermore, it has already been seen that the scala media is 
contained in a spirally-coiled chamber, the cochlea^ which it 
divides into two passages. Of these, one, the scala vesiibuli, 
is so called because it opens directly into the vestibule ; and 
hence it is that the perilymph fills these scalse as w^ell as the 
vestibule and semicircular canals, the whole being placed in 
communication by the wide aperture which leads from the 
vestibule into the scala vestibuli. 

In the fresh state, the bony labyrinth, as this collection of 
cavities in the petrous bone is termed, is perfectly closed ; but 
in the dry skull there are two wide openings, termed fenestrce, 

Co. 




\u.Jid:.. 



Fig. so. 
Transverse section tbrough the side walls of the skull to show the parts of the ear.-- 
Co. Concha or external ear; E.3L external auditory meatus; Ty.M. tympanic 
membrane : Inc. Mall, incus and malleus ; A.S.C. .^E.S.^C, P.S. C. anterior, posterior, 
and external semicircular canals; <7oc. cochlea; Eu. Eustachian tube; 7.3/. in- 
ternal auditory meatus, through which the auditory nerve passes to the organ of 
hearing. 



THE MECHANISM OF HEARING. 193 

or windows, on its outer wall. Of these fenestra), one, termed 
ovalis (the oval window), is situated in the wall of the ves- 
tibular cavity ; the other, rotunda (the round window), behind 
and below this, is the open end of the scala cochlece. In the 
fresh state, each of these windows, or fenestras, is closed by 
a fibrous membrane continuous with the periosteum of the 
bone. 

The fenestra rotunda is closed only by membrane ; but 
fastened to the centre oiiha fenestra ovalis^ so as to leave only 
a narrow margin, is an oval plate of bone, the base of the stapes 
or stirrup-bone. 

254. Tympanum and Eustachian Tube. — The outer wall 
of the bony labyrinth is still far away from the exterior of the 
skull. Between it and the visible opening of the ear, in fact, 
are placed in a straight line, first, the drum of the car, or 
tympanum ; secondly, the long external passage, or meatus 
(Fig. 80). 

The drum of the ear and the external meatus would form 
one cavity, were it not that a delicate membrane, the tympanic 
membrane [Ty. M.), is tightly stretched in an oblique direc- 
tion, across the passage, so as to divide the comparatively 
small cavity of the drum from the meatus. 

The membrane of the drum thus prevents any communica- 
tion between the drum and the exterior, by means of the me- 
atus, but such a communication is provided, though in a round- 
about way, by the Eustachian tube (Uu, Fig. 80), which leads 
directly from the fore part of the drum inward to the roof of 
the pharynx, where it opens. 

255. The Auditory Ossicles.— Three small bones, the au- 
ditory ossicles, lie in the cavity of the tympanum. One of these 
is the siajjcs, a small bone shaped like a stirrup. The foot- 
plate of this bone is, as already mentioned, firmly fastened to 
the membrane of the fenestra ovalis, while its hoop pr(:>jects 
inward into the tympanic cavity (Fig. 82). 

Another of these bones is the malleus {Mall. Figs. 80, 82), 
or hammer-bone, a long process of which is similarly iiistened 



194 



ELEMENTARY PHYSIOLOGY. 



to the inner side of the tympanic membrane (Fig. 81). The 
rounded surface of the head of the malleus fits into a corre- 
sponding pit in the other end of the third bone, the incus or 
anvil-bone, which has two processes — one, horizontal, which 
rests upon a support afforded to it by the w^alls of the tympa- 
num ; while the other, vertical, descends almost parallel with 
the long process of the malleus, and articulates with the stapes, 
or rather with a little bone, the os orhiculare wdiich is united 
with the stapes (Figs. 81, 82). 




Fig. 81. 

The membrane of the drum of the ear seen from the inner side, with the small hones 
of the ear; and the walls of the tj'mpanimi, with the air-cells in the mastoid part 
of the temporal bone.— ^/. 6". Mastoid cells; 3Iall. malleus; Inc. incus; Si, 
stapes; a b, lines drawn thiongh the horizontal axis on which the malleus and 
incus turn. 

The three bones thus form a chain between the fenestra 
ovalis and the tympanic membrane; and the whole series 
turns upon a horizontal axis, the two ends of which, formed 
by the horizontal process of the incus and the slender pro- 
cess of the malleus, rest in the walls of the tympanum. 
The general direction of this axis is represented by the 
line a h in Fig. 81, or by a line perpendicular to the plane 
of the paper, passing through the head of the malleus in Fig. 
82. -It follows, thei-efore, that whatever causes the membrane 
of the drum to vibrate backward and forward, must force the 
handle of the malleus to travel in the same way. This must 
cause a corresponding motion of the long process of the incus. 



THE MECHANISM OF HEARING. 



195 



the end of which must drag the stapes backward and forward. 
And, as this is fastened to the membrane of the fenestra ovalis, 
which is in contact with the perilymph, it must set this fluid 
vibrating throughout its whole extent, the thrastings in of the 




Fig. 82. 

A diagram illustrative of the relative positions of the various parts of the ear.—R J/. 
external auditory meatus ; Ti/. J/, tympanic membrane ; 7"^. tympanum ; Jfall, 
malleus; Inc. incus; Stp. stapes; F.o. fenestra ovalis; F.r: fenestra rotunda; 
Ell. Eustachian tube, 31. L. membranous labyrinth, only one semicircular canal 
with its ampulla being represented; Sea. F!, Sea. 71, hca. M. the scalar of the 
cochlea, which is supposed to be unrolled. 

membrane of the fenestra ovaUs being compensated by cor- 
responding thrustings out of the membrane of the fenestra 
rotunda, and vice versa. 

The vibrations of the perilymph thus produced will affect 
the endolymph, and this the otolithes ; by which, finally, the 
auditory nerves will be excited. 

256. The Muscles of the Tympanum. — The membrane of 
the fenestra ovalis and the tympanic membrane will necessarily 
vibrate the more freely the looser they are, and tlie revei-se. 
But there are two muscles — one, called the stapedius, which 
passes from the floor of the tympanum to the orbicular bone, 
and the other, the tensor tympanic from the front wall of the 



196 ELEMENTARY PHYSIOLOGY. 

drum to tlie malleus. Eacb of the muscles when it contracts 
tightens the membranes in question, and restricts their vibra- 
tions ; or, in other words, tends to check the effect of any 
cause which sets these membranes vibrating. 

257. The Concha. — The outer extremity of the external 
meatus is surrounded by the concha or external ear (Fig. 80, 
(7o.), a broad, peculiarly-shaped, and, for the most part, carti- 
laginous plate, the general plane of which is at right angles 
with that of the axis of the auditory opening. The concha can 
be moved in various directions by muscles which pass to it 
from the side of the head. 

Section IV. — Working of the Auditory Mechanism, 

258. Nature of Sound. — ^The manner m which the com- 
plex apparatus now described intermediates between the physi- 
cal agent, which is the condition of the sensation of sound, and 
the nervous expansion, the affection of which alone can excite 
that sensation, must now be considered. 

All bodies which produce sound are in a state of vibration, 
and they communicate the vibrations of their own substance 
to the air with which they are in contact, and thus throw that 
air into waves, just as a stick waved backward and forward in 
water throws the water into waves. 

The aerial waves, produced by the vibrations of sonorous 
bodies, in part enter the external auditory passage, and in part 
strike upon the concha of the external ear and the outer sur- 
face of the head. It may be that some of the latter impulses 
are transmitted through the solid structure of the skull to the 
organ of hearing; but before they reach it they must, under 
ordinary circumstances, have become so scanty and weak, that 
they may be left out of consideration. 

The aerial waves which enter the meatus all impinge upon 
the membrane of the drum and set it vibrating, stretched 
membranes taking up vibrations from the air with great readi- 
ness. 



WORKING OF THE AUDITORY MECHANISM. 197 

259. Vibrations of the Tympanum. — The vibrations thus 
set up in the membrane of the drum are communicated, in 
part, to the air contained in the drum of the ear, and, in part, 
to the malleus, and thence to the other auditory ossicles. 

The vibrations communicated to the air of the drum im- 
pinge upon the inner wall of the tympanum, on the greater 
part of which, from its density, they can produce very little 
effect. Where this wall is formed by the membrane of the 
fenestra rotunda^ however, the communication of motion must 
necessarily be greater. 

The vibrations which are communicated to the malleus and 
the chain of ossicles may be of two kinds : vibrations of the 
particles of the bones, and vibrations of the bones as a whole. 
If a beam of wood, freely suspended, be very gently scratched 
with a pin, its particles will be thrown into a state of vibra- 
tion, as will be evidenced by the sound given out, but the 
beam itself will not be moved. But, if a strong wind blow 
against the beam, it will swing visibly, without any vibrations 
of its particles among themselves. On the other hand, if the 
beam be sharply struck with a hammer, it will not only give 
out a sound, showing that its particles are vibrating, but it will 
also swing, from the impulse given to its whole mass. 

Under the last-mentioned circumstances a blind man stand- 
ing near the beam would be conscious of nothing but the 
sound, the Droduct of molecular vibration, or invisible oscilla- 
tion of the particles of the beam ; while a deaf man, in the 
same position, would be aware of nothing but the visible oscil- 
lation of the beam as a whole. 

260. Their Transmission, — Thus, to return to the chain 
of auditory ossicles, while it seems hardly to be doubted that, 
when the membrane of the drum vibrates, they are set vibrat- 
ing both as a whole and in their particles, it depends upon 
subsidiary arrangements whether the large vibrations, or the 
minute ones, shall make themselves obvious to the auditory 
nerve, which is in the position of our deaf, or blind, man. 

The evidence at present is in favor of the conclusion, that 



198 ELEMENTARY PHYSIOLOGY. 

it is the vibrations of the bones, as a whole, which are the 
chief agents in transmitting the impulses of the aerial waves. 

For, in the first place, the disposition of the bones and the 
mode of their articulation are very much against the trans- 
mission of molecular vibrations through their substance, while, 
on the other hand, they are extremely favorable to their vi- 
bration en masse. The long processes of the malleus and 
incus swing, like a pendulum, upon the axis furnished by the 
short processes of these bones; while the mode of connection 
of the incus with the stapes, and of the latter with the edges 
of the fenestra ovalis, allows of free play, inward and outward, 
to that bone. And, in the second place, it is affirmed, as the 
result of experiments, that the bone called columella^ which, in 
birds, takes the place of the chain of ossicles in man, does 
actually vibrate as a whole, and at the same rate as the mem- 
brane of the driira, when aerial vibrations strike upon the latter. 

261. The Action of the Auditory Muscles. — Thus, there 
is reason to believe that when the tympanic membrane is set 
vibrating, it causes the process of the malleus, which is fixed 
to it, to swing at the same rate; the head of the malleus con- 
sequently turns through a small arc on its pivot, the slender 
process. But the turning of the head of the malleus involves 
that of the head of the incus upon its pivot, the short process. 
In consequence, the long process of the incus swings through 
an arc as nearly as possible equal to that described by the 
handle of the malleus. But the long process is so fixed to the 
stapes that it cannot vibrate without, to a corresponding ex- 
tent and at the same rate, pulling this out of, and pushing it 
in to, the fenestra ovalis. But every pull and push imparts a 
corresponding set of shakes to the perilymph, which fills the 
bony labyrinth and cochlea, external to the membranous laby- 
rinth and scala media. These shakes are communicated to the 
endolymph and fluid of the scala media, and, by the help of 
the otolithes and the fibres of Corti, are finally converted into 
impulses, which act as irritants to the ends of the vestibular 
and cochlear divisions of the auditorv nerve. 



WORKING OF THE AIJDITOKY MECHANISM. 199 

262. Intensity and Quality of Sounds— how discrim- 
inated. — The difference between the fiinctions of the mem- 
branous labyrinth (to which the vestibular nerve is distributed) 
and those of the cochlea are, perhaps, not quite so certainly- 
made out, but the following conclusions are highly probable : 

The membranous labyrinth is an apparatus whereby sounds 
are appreciated and distinguished according to their intensity 
or quantity ; but it does not afford any means of discriminating 
their qualities. The vestibular nerve tells us that sounds are 
low or loud, but gives us no impression of tone, or melody, or 
harmony. 

The cochlea, on the other hand, discriminates the quality 
rather than the quantity or intensity of sound. There is great 
reason to believe that the excitement of any single filament of 
the cochlear nerve gives rise, in the mind, to a distinct musical 
impression ; and that every fraction of a tone which a well- 
trained ear is capable of distinguishing, is represented by its 
separate nerve-fibre. Thus, the scala media resembles a key- 
board, in function, as well as in appearance, the fibres of Corti 
being the keys, and the ends of the nerves representing the 
strings which the keys strike. If it were possible to irritate 
each of these nerve-fibres experimentally, we should be able to 
produce any musical tone, at will, in the sensorium of the per- 
son experimented upon, just as any note on a piano is pro- 
duced by striking the appropriate key. 

263. Probable Function of the Fibres of Corti. — A tuning- 
fork may be set vibrating, if its own particular note, or one 
harmonic with it, be sounded in its neighborhood. In other 
words, it will vibrate under the influence of a particular set of 
vibrations, and no others. If the vibrating ends of the tuning- 
fork were so arranged as to impinge upon a nerve, their re- 
peated minute blow^s would at once excite this nerve. 

Suppose that of a set of tuning-forks, tuned to every note and 
distinguishable fraction of a note in the scale, one wore thus 
connected with the end of every fibre of the cochlear nerve ; 
then any vibration communicated to the perilymph would 



200 ELEMENTARY PHYSIOLOGY. 

affect the tuning-fork wliich could vibrate with it, while the 
rest would be absolutely, or relatively, indifferent to that vibra- 
tion. In other words, the vibration would give rise to the 
sensation of one particular tone, and no other, and every mu- 
sical interval would be represented by a distinct impression on 
the sensorium. 

It is believed that the fibres of Corti are competent to per- 
form the function of such tuning-forks ; that each of them is 
set vibrating to its full strength by a particular kind of wave 
sent through the perilymph, and by no other ; and that each 
affects a particular fibre of the cochlear nerve only. 

The fibres of the cochlear nerve may be excited by internal 
causes, such as the varying pressure of the blood and the like. 
And in some persons such internal influences do give rise to 
veritable musical spectra, sometimes of a very intense character. 
But for the appreciation of music produced external to us, we 
depend upon the intermediation of the scala media and its 
Cortian fibres. 

264. Function of the Tympanic Muscles and Eustachian 
Tube. — It has already been explained that the stapedius and 
tensor tympani muscles are competent to tighten the membrane 
of the fenestra ovalis and that of the tympanum, and it is 
probable that they come into action when the sonorous im- 
pulses are too violent, and would produce too extensive 
vibrations of these membranes. They therefore tend to mod- 
erate the effect of intense sound, in much the same way that, 
as we shall find, the contraction of the circular fibres of the 
iris tends to moderate the efiect of intense light in the eye. 

The function of the Eustachian tube is, probably, to keep 
the air in the tympanum, or on the inner side of the tympanic 
membrane, of about the same tension as that on the outer side, 
which could not always be the case if the tympanum were a 
closed cavity. 



STRUCTUKE AND ACTION OF THE EETINA. 201 

CHAPTER X. 

THE OEGAN OF SIGHT. 

Section I. — Structure and Action of the Retina. 

265. General Structure of the Eye. — In studying the 
organ of the sense of sight, the eye, it is needful to become 
acquainted, firstly, with the sensory expansion in which the 
optic nerve terminates, and its properties ; secondly, with the 
physical agent of the sensation; thirdly, with the intermediate 
apparatus by which the physical agent is enabled to act upon 
the nervous expansion. 

The ball of the eye is a globular body, moving freely in a 
chamber, the orhit^ which is furnished to it by the skull. The 
optive nerve, the root of which is in the brain, leaves the skull 
by a hole at the back of the orbit, and enters the back of the 
globe of the eye, not in the middle, but on the inner, or nasal, 
side of the centre. It then spreads out on the inner surface 
of the wall of the globe of the eye into a very delicate layer, 
varying in thickness from -gV^h of an inch to less than half that 
amount, which is termed the retina. This retina is the only 
termination of sensory nervous fibres which can be affected, 
by any agent, in such a manner as to give rise to the sensa- 
tion of light. 

266. The Surface of the Retina.— If the globe of the eye 
be cut in two, transversely, so as to divide it into an anterior 
and a posterior half, the retina will be seen lining the concave 
wall of the posterior half as a membrane of great delicacy, and, 
for the most part, of even texture and smooth surface. But, 
exactly opposite the middle of the posterior wall it presents a 
slight circular depression of a yellowish hue, the macula lutca, 
or yellow spot; and at some distance from this, toward the 
inner, or nasal, side of the ball, is a radiatino* appearance, pro- 



202 



ELEMENTARY PHYSIOLOGY. 



ducecl by the entrance of the optic nerve and the spreading out 
of its fibres into the retina. 

267, Microscopic Structure of the Retina. — A vertical 
section of the retina, in any region except the yellow spot and 
the entrance of the optic nerve, presents the appearance repre- 
sented in Fig. 83. On its inner side, a, it is bounded by a 




Fig. 83. 

A vertical section of the retina — a. The limiting membrane next io the vitreous 
Ijtimor ; h, the layer of ganglionic corpuscles ; between these the fibres of the optic 
nerve, which are cut across in this section, run ; c, the inner layer of granules; 
d, the outer layer of gy^inules separated by the intergranular layer. The in- 
terval between h and c is the finely-granular layer; e is the layer of rods and 
cones in immediate contact, with the choroid by their outer ends. The vessels 
ramify between a and c. The fine vertical lines running through all the layers 
from the cones and rods are the radial fibres, which spread out fan-wise as they 
near the limiting membrane. The total thickness of the section here figured 
does not exceed «^oth of an inch. 



structureless membrane, the limiting memh^ane^ which separates 
it from the vitreous humor ^ with which we shall hereafter be- 
come acquainted. Externally it consists of a vast multitude of 
minute, rod-like, and conical bodies, ranged side by side, per- 
pendicularly to the plane of the retina. This is the layer of 
rods and cones, and occupies about a quarter of the whole thick- 
ness. From the inner ends of the rods and cones very deli- 



STEUCTUKE AND ACTION OF THE RETINA. W6 

cate radial fibres pass and spread out into branches, whicL. 
are continued into the limiting membrane. Between the layer 
of rods and cones and the limiting membrane, and interposed 
between the radial fibres, are layers of gTanules d, c ; while at 
b there is a layer of ganglionic corpuscles with ramified pro- 
cesses. It is of less importance to remember these circum- 
stances, however, than the facts, that the fibres of the optic 
nerve spread out between the limiting membrane (a) and the 
ganglionic corpuscles (5) ; and that the vessels which enter 
along with the optic nerve ramify between the limiting mem- 
brane and the layer c. Thus, not only the nervous fibres, but 
the vessels, are placed altogether in front of the rods and cones. 

At the entrance of the optic nerve itself the nervous fibres 
predominate, and the rods and cones are absent. In the yel- 
low spot, on the contrary, the cones are abundant and close 
set, without the interposition of rods, and the nervous fibres 
disappear. 

268. The Sensation of Light. — The most notable property 
of the retina is its power of converting the vibrations of ether, 
which constitute the physical basis of light, into a stimulus to 
the fibres of the optic nerve — ^which fibres, when excited, have 
the power of awakening the sensation of light in, or by in cans 
of, the brain. The sensation of light, it must be understood, is 
the work of the brain, not of the retina; for if an eye be de- 
stroyed, pinching, galvanizing, or otherwise irritating the optic 
nerve, will still excite the sensation of light, because it throws 
the fibres of the optic nerve into activity ; and their activity, 
however produced, bring-s about in the brain certain changes 
which give rise to the sensation of light. 

Light, falling on the optic nerve, does not excite it ; the 
fibres of the optic nerve, in themselves, are as blind as any 
other part of the body. But just as the delicate filaments of 
the ampullse, or the otoconia of the vestibular sac, or the Cor- 
tian fibres of the cochlea, are contrivances for converting the 
delicate vibrations of the perilymph and endolymph into 
impulses which can excite the auditory nerves, so the struc- 



204: ELEMENTARY PHYSIOLOGY. 

tares in the retina appear to be adapted to convert the infinitely 
more delicate piilses of the luminiferous ether into stimuli of 
the fibres of the optic nerve. 

269. The "Blind Spot"— The sensibility of the diff*erent 
parts of the retina to light varies very greatly. The point of 
entrance of the optic nerve is absolutely blind, as may be proved 
by a very simple experiment. Close the left eye, and look 
steadily with the right at the cross on the page, held at ten or 
twelve inches' distance. 

The black dot will be seen quite plainly, as well as the cross. 
Now, move the book slowly toward the eye, which must be 
kept steadily fixed upon the cross; at a certain point the dot 
will disappear, but as the book is brought still closer it will 
come into view again. It results from optical principles that, 
in the first position of the book, the figure of the dot falls be- 
tween that of the cross (which throughout lies upon the yellow 
spot) and the entrance of the optic nerve ; while, in the second 
position, it falls on the entrance of the optic nerve itself; and, 
m the third, inside that point. So long as the image of the 
spot rests upon the entrance of the optic nerve it is not per- 
ceived, and hence this region of the retina is called the blind 
spot, 

270. Duration of Luminous Impressions. — The impres- 
sion made by light upon the retina is not merely coexistent 
with the time the light aff^ects it, but has a certain duration of 
its own, however short the time during which the light itself 
lasts. A flash of lightning is, practically, instantaneous, but 
the sensation of light produced by that flash endures for an 
appreciable period. It is found, in fact, that a luminous im- 
pression lasts for about one-eighth of a second ; whence it fol- 
lows, that if any two luminous impressions are separated by a 
less interval, they are not distinguished from one another. 

For this reason a "Catherine-wheel," or a lighted stick 
turned round very rapidly by the hand, appears as a circle of 



STRUCTURE AND ACTION OF THE RETINA. 205 

fire ; and the spokes of a coacli-whecl at speed are not sepa- 
rately visible, but only appear as a sort of opacity, or film, 
within the tire of the wheel. 

271. Exhaustion of the Retina. — The excitability of the 
retina is readily exhausted. Thus, looking at a bright light 
rapidly renders the part of the retina on which the light falls, 
insensible ; and on looking from the bright light toward a 
moderately-lighted surface, a dark spot, arising from a tempo- 
rary blindness of the retina in this part, appears in the field of 
view. If the bright light be of one color, the part of the retina 
on which it falls becomes insensible to rays of that color, but 
not to the other rays of the spectrum. This is the explanation 
of the appearance of what are called complementary colors. 
For example, if a bright-red wafer be stuck upon a sheet of 
white paper, and steadily looked at for some time with one eye, 
when the eye is turned aside to the white paper, a greenish 
spot will appear of the size and shape of the wafer. The red 
image has, in fact, fatigued the part of the retina on which it 
fell for red light, but has left it sensitive to the remaining colored 
rays of which white light is composed. So that, when white 
light falls upon this part, the red rays in the white light have no 
effect, and the result of the operation of the others is a greenish 
hue. If the wafer be green^ the complementary image^ as it is 
called, is red. 

272. Color Blindness. — In some persons the retina appears 
to be affected in one and the same way by rays of light of 
various colors, or even of all colors. Such color-blind persons 
are unable to distinguish between the leaves of a cherry-tree 
and its fruit by the color of the two, and see no difference be- 
tween blue and yellow cloth. 

This peculiarity, which is simply unfortunate for most per- 
sons, but may be dangerous if unknowingly possessed by rail- 
way guards or sailors, may arise either from a defect in the 
retina, which renders it unable to respond to different kinds of 
luminous vibrations, or it may proceed from some unusual 
absorptive power of the humors of the eye. 



206 ELEMENTARY PHYSIOLOGY. 

273. Luminous Effects of Pressure on the Eye. — The 

sensation of light may be excited by other causes than the im- 
pact of the vibrations of the luminiferous ether upon the retina. 
Thus, an electric shock sent through the eye gives rise to an 
apparent flash of light ; and pressure on any part of the retina 
produces a luminous image, which lasts as long as the pressure, 
and is called aphosphene. If the point of the finger be pressed 
upon the outer side of the ball of the eye, a luminous image is 
seen— which, in my own case, is dark in the centre, with a 
bright ring at the circumference (or as Newton described it, 
like the " eye " in a peacock's tail) — and this image lasts as 
long as the pressure is continued. Most persons, again, have 
experienced the remarkable display of subjective fireworks 
which follows a heavy blow upon the eyes, produced by a fall 
from a horse, or by other methods well known to English youth. 
It is doubtful, however, whether these effects of pressure, or 
shock, really arise from the excitation of the retina proper, or 
w^hether they are not rather the result of the violence done to 
the fibres of the optic nerve apart from the retina. 

274. Function of the Rods and Cones. — The last para- 
graph raises a distinction between the "fibres of the optic 
nerve," and the " retina " which may not have been anticipated, 
but w^hich is of much importance. 

We have seen that the fibres of the optic nerve ramify in 
the inner fourth of the thickness of the retina, Avhile the layer 
of rods and cones forms its outer fourth. The light, therefore, 
must fall first upon the fibres of the optic nerve, and, only after 
traversing them, can it reach the rods and cones. Conse- 
quentl}^ if the fibrillse of the optic nerve themselves are capa- 
ble of being affected by light, the rods and cones can only be 
some sort of supplementary optical apparatus. But, in fact, it 
is the rods and cones which are aftected by light, w^hile the 
fibres of the optic nerve are themselves insensible to it. The 
evidence on which this statement rests is — 

a. The blind spot is full of nervous fibres, but has no cones 
or rods. 



THE LUMINOUS AGENT. 207 

b. The yellow spot, where the most acute vision is situated, 
is full of close-set cones, but has no nerve fibres, 

c. If you go into a dark room with a single small bright 
candle, and looking toward a dark wall, move the light up and 
down, close to the outer side of one eye, so as to allow the 
light to fall very obliquely into the eye, oue of what are called 
Ficrkinje^s figures is seen. This is a vision of a series of 
diverging, branched, red lines on a dark field, and in the inter- 
space of two of these lines is a sort of cup-shaped disk. The 
red lines are the retinal blood-vessels, and the disk is the yellow 
spot. As the candle is moved up and down the red lines shift 
their position, as shadows do when the light which throws 
them changes its place. 

Now, as the light falls on the inner face of the retina, and 
the images of the vessels to which it gives rise shift their posi- 
tion as it moves, whatever perceives these images must needs 
lie on the other, or outer, side of the vessels. But the fibres 
of the optic nerve lie among the vessels, and the only retinal 
structures which lie outside them are the granular layers and the 
rods and cones. 

Just as, in the skin, tliere is a limit of distance within which 
two points give only one impression ; so there is a minimum 
distance by which two points of light falling on the retina must 
be separated in order to appear as two. And this distance 
corresponds pretty well with the diameter of the cones. 

Thus it would appear that these remarkable structures, set 
upon the outer surface of the retina, with their ends turned 
toward the light, are like so many finger-points, endowed with 
a touch delicate enough to feel the luminous vibrations. 

Section IT. — The Luminous Agent 

275. The Convex Lens. — The physical agent which gives 
rise to vision is light ^ which is now conceived to bo a very 
attenuated fluid, the ether, vibrating in a particular way. The 
properties of this physical agent and the principles of optics 



208 ELEMENTAEY PHYSIOLOGY. 

must be studied elsewhere. At present it is only necessary to 
advert to some facts, of which every one can assure himself by 
simple experiments. An ordinary spectacle glass is a trans- 
parent body denser than the air, and convex on both sides. 
If this lens be held at a certain distance from a screen or wall 
in a dark room, and a lighted candle be placed on the oppo- 
site side of it, it will be easy to adjust the distances of candle, 
lens, and wall, so that an image of the flame of the candle, up- 
side down, shall be thrown upon the wall. 

276. Formation of the Lummoiis Picture. — The spot on 
which the image is formed is called the focus. If the candle 
be now brought nearer to the lens, the image on the wall will 
enlarge, and grow blurred and dim, but may be restored to 
brightness and definition by moving the lens farther from the 
wall. But if, when the new adjustment has taken place, the 
candle be moved away from the lens, the image will again be- 
come confused, and the lens will have to be brought nearer the 
wall to restore its clearness. 

Thus a convex lens forms a distinct picture of luminous 
objects, but only at its focus ; and that focus is nearer when the 
object is distant, and farther off when it is near. 

277. Effect of varjring the Convexity. — Suppose, how- 
ever, that, leaving the candle unmoved, a lens with more con- 
vex surfaces is substituted for the first, the image will be blurred, 
and the lens will have to be moved nearer the wall to give it 
definition. And if, on the other hand, a lens with less convex 
surfaces is substituted for the first, it must be moved farther 
from the wall to attain the same end. 

In other words, other things being alike, the more convex 
the lens the nearer its focus; the less convex, the farther off its 
focus. 

If the lens were elastic, pulling it at the circumference 
would render it flatter, and thereby lengthen its focus ; while, 
when let go again, it would become more convex, and of shorter 
focus. 

Any material more refractive than the medium in which it 



THE LUMINOUS AGENT. 209 

is placed, if it have a convex surface, causes the rays of liglit 
which pass through the less refractive medium to that surface 
to converge toward a focus. If a watch-glass be fitted into 
one side of a box, and the box be then filled with water, a 
candle may be placed at such a distance outside the watch- 
glass, that an image of its flame shall fall on the opposite wall 
of the box. If, under these circumstances, a doubly convex 
lens of glass were introduced into the water in the path of the 
rays, it would act (though less powerfully than if it were in 
air) in bringing the rays more quickly to a focus, because glass 
refracts light more strongly than water does. 

A camera ohscura is a box, into one side of which a lens is 
fitted, so as to be able to slide in and out, and thus throw dis- 
tinct images of bodies, at various distances, on the screen at 
the back of the box. Hence the arrangement just described 
might be termed a water camera. 

Section HI. — The Intermediate Apparatus. 

278. The Visual Mechanism. — The intermediate organs, 
by means of which the physical agent of vision, light, is en- 
abled to act upon the expansion of the optic nerve, comprise 
three kinds of apparatus : {a) A " water camera," the eyeball ; 
{h) muscles for moving the eyeball ; (c) organs for protecting 
the eyeball, viz., the eyelids, with their lashes, glands, and 
muscles; the conjunctiv^a ; and the lachrymal gland and its 
ducts. 

The cT/ehall is composed, in the first place, of a tough, firm, 
spheroidal case consisting of connective tissue, the greater part 
of which is white and opaque, and is called the sclerotic [Scl, 
Fig. 84). In front, however, this fibrous capsule of the eye, 
though it does not change its essential character, becomes 
transparent, and receives the name of the cornea [Cn, Fig. 84). 
The corneal portion of the case of the eyeball is more convex 
than the sclerotic portion, so that the whole form of the ball 
is such as would be produced by cutting oft' a segment from 



210 ELEMENTARY PHYSIOLOGY. 

the front of a spheroid of the diameter, of the sclerotic, and 
replacing this by a segment cut from a smaller, and conse- 
quently more convex, sphere. 

279. The Humors and Crystalline Lens, — The corneo- 
sclerotic case of the eye is kept in shape by what are termed 
the humors — watery or semi-fluid substances, one of which, 
the aqueous humor, distends the corneal chamber of the eye, 
while the other, the vitreous^ keeps the sclerotic chamber full. 

The two humors are separated by the very beautiful, trans- 
parent, doubly convex crystalline lens {Cry, Fig. 84), denser 
and capable of refracting light more strongly, than either of 
the bumors. The crystalline lens is composed of fibres having 
a somewhat complex arrangement, and is highly elastic. It is 
more convex behind than in front, and it is kept in place by a 
delicate, but at the same time strong and elastic, membranous 
frame or susj^ensory ligament, which extends from the edges 
of the lens to what are termed the ciliary processes of the cho- 
roid coat. 

280. The Choroid and Ciliary Processes.— This choroid 
coat ( Ch, Fig. 84) is a highly vascular membrane, in close con- 
tact with the sclerotic externally, and lined, internally, by a 
layer of small polygonal bodies containing much pigmentary 
matter, o^sW^di pigment-cells. These pigment-cells are separated 
from the vitreous humor by the retina only. The rods and 
cones of the latter are in immediate contact with them. The 
choroid lines every part of the sclerotic, except where the op- 
tic nerve enters it, at a point below, and to the inner side of 
the centre of the back of the eye ; but when it reaches the 
front part of the sclerotic its inner surface becomes raised up 
into a number of longitudinal ridges, with intervening depres- 
sions, terminating within and in front by rounded ends, but 
passing, externally, into the iris. These ridges are the ciliary 
processes {C.jx Fig. 84). 

281. The Iris and Ciliary Muscle. — The iris itself 
(Ir, Fig. 84) is, as has already been said, a curtain with a 
round hole in the middle, provided with circular and radiating 



THE mXERMEDIATE APPARATUS. 211 

unstriped muscular fibres ; and capable of having its central 
aperture enlarged or diminished by the action of these fibres, 
the contraction of which is extremely rapid. The edges of the 
iris are firmly connected with the capsule of the eye, at the 
junction of the cornea and sclerotic, by the connective tissue 
which enters into the composition of the so-called ciliary lig- 
ament Unstriped muscular fibres, having the same attach- 
ment in front, spread backward on to the outer surface of the 
choroid, constituting the ciliary muscle [Cm, Fig. 84). If 
these fibres contract, it is obvious that they will pull the 
choroid forward ; and, as the frame, or suspensory ligament, 
of the lens is connected with the ciliary processes (which 
simply form the anterior termination of the choroid), this pull- 
ing forward of the choroid comes to the same thing as a relax- 
ation of the tension of that suspensory ligament, which, as I 
have just said, like the lens itself, is highly elastic. 

The iris does not hang down perpendicularly into the 
space between the front face of the crystalline lens and the 
posterior surface of the cornea, which is filled by the aqueous 
humor, but applies itself very closely to the anterior face of the 
lens, so that hardly any space is left between the two (Figs. 
84, 85). 

Section IV. — Focal Adjustment 

282. The Iris a Self-regulating Diaphragm. — The eye- 
ball, the most important constituents of which have now been 
described, is, in principle, a camera of the kind described 
above — -a water camera. Tliat is to say, the sclerotic answers 
to the box, the cornea to the watch-glass, the aqueous and vitre- 
ous humors to the water filling the box, the crystalline to the 
glass lens, the introduction of which was imagined. The back 
of the box corresponds with the retina. 

But further, in an ordinary camera obscura, it is found de- 
sirable to have what is termed a diaphragm (that is, an opaque 
plate with a hole in its centre) in the path of the rays, for the 



212 



ELEMENTARY PHYSIOLOGY. 



purpose of moderating the light and cutting off the marginal 
rays which, owing to certain optical properties of spheroidal 
surfaces, give rise to defects in the image formed at the focus. 
In the eye, the place of this diaphragm is taken by the 
iris, which has the pecuHar advantage of being self-regulatmg ; 




Horizontal section of the eyeball.— /Sc?. The sclerotic coat; Cn. the cornea; R. the at- 
tachments of the tendons of the recti muscles; Ch. the choroid: C.p. the ciliary 
processes; Cm. the ciliary muscle ; Ir. the iris; Aq. the aqueous humor: Cry. 
the crystalline lens; Vt. the vitreous humor; Et. the retina; Op. the optic nerve; 
311. the yellow spot. The section has passed through a ciliary process on the left 
side, and between two ciliary processes on the right. 



dilating its aperture and admitting more hght when the light 
is weak ; but contracting its aperture and admitting less light 
when the illumination is strong. 

283. Necessity of Adjustment. — In the water camera, con- 
structed according to the description given above, there is the 
defect that no provision exists for adjusting the focus to the 
varying distances of objects. If the box were so made that its 
back, on which the image is supposed to be thrown, received 
distinct images of very distant objects, all near ones would be 



FOCAL ADJUSTMENT. 213 

indistinct. And if, on the other hand, it were fitted to receive 
the image of near objects, at a given distance, those of either 
nearer, or more distant, bodies would be bhirred and indis- 
tinct. In the ordinary camera this difficulty is overcome by 
sliding the lenses in and out, a process which is not compati- 
ble with the construction of our water camera. But there is 
clearly one way, among many, in which this adjustment might 
be effected — namely, by changing the glass lens; putting in a 
less convex one when more distant objects had to be pictured, 
and a more convex one when the images of nearer objects were 
to be thrown upon the back of the box. 

But it would come to the same thing, and be much more 
convenient, if, without changing the lens, one and the same 
lens could be made to alter its convexity. This is actually 
what IS done in the adjustment of the eye to distances. 

284. Experiment — Adjustment requires Effort. — The 
simplest way of experimenting on the adjustment of the eye is 
to stick two stout needles upright into a straight piece of wood, 
not exactly, but nearly in the same straight line, so that, on 
applying the eye to one end of the piece of wood, one needle 
(a) shall be seen about six inches off, and the other {b) just on 
one side of it at twelve inches' distance. 

If the observer look at the needle h he will find that he sees 
it very distinctly, and without the least sense of effort ; but the 
image of a is blurred and more or less double. Now, let him 
try to make this blurred image of the needle a distinct. He 
will find he can do so readily enough, but that the act is ac- 
companied by a sense of fatigue. And furthermore, in pro- 
portion as a becomes distinct, h will become blurred. Nor 
will any effort enable him to see a and h distinctly at the same 
time. 

285. The Mechanism of Adjustment explained. — ^Mul- 
titudes of explanations have been given of this remarkable 
power of adjustment, but it is only within the last few years that 
the problem has been solved, by the accurate determination of 
the nature of the changes in the eye which accompany the act. 



2M 



ELEMENTARY PHYSIOLOGY. 



When tlie flame of a taper is held near, and a little on one side 
of, a person's eye, any one looking into the eye from a proper 
point of view will see three images of the flame, two upright 
and one inverted. One upright image is reflected from the 
front of the cornea, which acts as a convex mirror. The second 
proceeds from the front of the crystalline lens, which has the 
same eff'ect ; while the inverted image proceeds from the pos- 
terior face of the lens, which, being convex backward, is, of 
course, concave forward, and acts as a concave mirror. 

Suppose the eye to be steadily fixed on a distant object, 
and then adjusted to a near one in the same line of vision, the 
position of the ball, of course, remains unchanged. Further- 
more, the upright image reflected from the surface of the cor- 
nea, and the inverted image from the back of the lens, remain 
unchanged, though it is demonstrable that their size or appar- 
ent position must change if either the cornea, or the back of 
the lens, alter either their form or their position. But the 
second upright image, that reflected by the front face of the 
lens, changes both its size and its position ; and that in such a 
manner as to prove that the front face of the lens has become 
more convex. The change of form of the lens is, in fact, that 
represented in Fig. 85. 




Illustrates the change in the form of the lens when adjusted — A to distant, B to near 

objects. 



These may be regarded as the facts of adjustment with 
which all explanations of that process must accord. They at 
once exclude the hypotheses (1) that adjustment is the result 
of the compression of the ball of the eye by its muscles, which 
would cause a change in the form of the cornea; (2) that ad- 



FOCAL ADJUSTMENT. 215 

justment results from a shifting of the lens bodily, for its 
hinder face does not move ; (3) that it results from the pres- 
sure of the iris upon the front face of the lens, for under these 
circumstances the hinder face of the lens would not remain 
stationary. This last hypothesis is further negatived by the 
fact that adjustment takes place equally well when the iris is 
absent. 

One other explanation remains, which is, in all probability, 
the true one, though not altogether devoid of difficulties. The 
lens, which is very elastic, is kept habitually in a state of ten- 
sion by the elasticity of its suspensory ligament, and conse- 
quently has a flatter form than it would take if left to itself. If 
the ciliary muscle contracts, it must, as has been seen, relax 
that ligament, and thereby diminish its elastic tension upon 
the lens. The lens, consequently, will become more convex, 
returning to its former shape when the ciliary muscle ceases to 
contract, and allows the choroid to return to its ordinary 
place. 

If this be the true explanation of adjustment, the sense of 
effort we feel must arise from the contraction of the ciliary 
muscle. 

286. Limits of the Power of Adjustment. — Adjustment 
can take place only within a certain range, which admits of 
great individual variations. As a rule, no object which is 
brought within less than about ten inches of the eye can be 
seen distinctly without effort. 

But many persons are born with the surface of the cornea 
more convex than usual, or with the refractive power of the 
eye increased in some other way ; while, very generally, as age 
draws on, the cornea flattens. In the former case, objects at 
ordinary distances are seen indistinctly, because these images 
fall not on the retina, but in front of it ; while, in the latter, 
the same indistinctness is the result of the rays of light striking 
upon the retina before they have been brought to a focus. The 
defect of the former, or short-sighted people, is amended by 
wearing concave glasses, which cause the rays to diverge ; of 



216 



ELEMENTARY PHYSIOLOGY. 



the latter, or long-siglited people, by wearing convex glasses, 
which make the rays converge. 

Section Y. — Appendages of the Eyeball. 

287. Action of the Muscles of the Eyeball. — The muscles 
which nio^e the eyeball are altogether six in number — four 
straight muscles, or recti^ and two oblique muscles, the ohliquL 
The straight muscles are attached to the back of the orbit, 
round the edges of the hole through which the optic nerve 
passes, and run straight forward to their insertions in the 
sclerotic — one, the sup>erior rectus, in the middle line above ; 
one, the inferior, opposite it below ; and one half way on each 
side, the external and internal recti. The eyeball is completely 
imbedded in fat behind and laterally ; and these muscles turn 




c.k. m 



Fig. 86. 



The muscles of the eyeball viewed fi-om above and from the outer side. — S. B. the 
superior rectus;'/;?/. ^. the interior rectus; E.R. the external rectus; In. R. 
the internal rectus ; 5. Ob. the superior oblique ; Inf. Oh. the inferior oblique ; 
Ch. the chiasma of the optic nerves {IT.) ; /// the third nerve which supplies all 
the muscles except the superior oblique and the external rectus. 



it as on a cushion, the superior rectus inclining the axis of the 
eye upward, the inferior downward, the external outward, the 
internal inward. 

The two oblique muscles are both attached on the outer 
side of the ball, and rather behind its centre ; and they both 



APPENDAGES OF THE EYEBALL. 217 

pull in a direction from the point of attachment toward the 
inner side of the orbit — the lower, because it arises here ; the 
upper, because though it arises along with the recti from the 
back of the orbit, yet after passing forward, and becoming ten- 
dinous at the upper and inner corner of the orbit, it passes 
through a pulley-like loop of ligament, and then turns down- 
ward and outward to its insertion. The action of the oblique 
muscles is somewhat complicated, but their general tendency 
is to roll the eyeball on its axis and pull it a little forward and 
inward. 

288. The Eyelids. — The eijelids are folds of skin containing 
thin plates of cartilage, and fringed at their edges with hairs, 
the eyelashes, and with a series of small glands called Meibo- 
mian, Circularly disposed fibres of striped muscle lie beneath 
the integuments of the eyelids, and constitute the obicularis 
muscle which shuts them. The upper eyelid is raised by a 
special muscle, the levator of the upper lid, which arises at the 
back of the orbit and runs forward to end in the lid. 

The lower lid has no special depressor. 

289. The Lachrymal Apparatus. — At the edge of the 
eyelids the integument becomes continuous with a delicate, 
vascular, and highly nervous mucous membrane, the conjunc- 
tiva, which lines the interior of the lids and the front of the 
eyeball, its epithelial layer being even continued over the 
cornea. The numerous small ducts of a gland which is lodged 
in the orbit, on the outer side of the ball (Fig. 88), the lachry- 
mal gland, constantly pour its watery secretion into the inter- 
space between the conjunctiva lining the upper eyelid and that 
covering the ball. On the inner side of the eye is a reddish 
fold, the caruncula lachrymalis, a sort of rudiment to the third 
eyelid, which is to be found in many animals. Above and 
below, the edge of each eyelid presents a minute aperture (the 
punctwn hchnjmale), the opening of a small canal. The canals 
from above and below converge and open into the lachrymal 
sac, the upper blind end of a duct (Z. i).) which passes down 
from the orbit to the nose, opening below the inferior turbinal 

10 



218 



ELEMENTARY PHYSIOLOGY. 



bone (Fig. 53, h). It is through this system of canals that the 
conjunctival mucous membrane is continuous with that of the 




%rOr&» 



TtiJ^06. 



Fig. 87. 

A front view of the eye dissected to show— 6)rft., the orbicular muscle of the eyelids ; 
the pulley and insertion of the superior oblique, 8. Ob.^ and the inferior oblique, 
Inf. Oh. ; L. G. the lachrymal gland. 

nose ; and it is by them that the secretion of the lachrymal 
canal is ordinarily carried away as fast as it forms. 

But, under certain circumstances, as when the conjunctiva 




m^-<^- 



xa>. 



Fig. 88. 

A front view of the eye, with the eyelids.— Lachrymal gland, Z. G.^ and Lachrymal 
duct, L. D, 



is irritated by pungent vapors, or when painful emotions arise 
in the mind, the secretion of the lachrymal gland exceeds the 
drainage power of the lachrymal duct, and the fluid, accumu- 
lating between the lids, at length overflows in the form of 
tears. 



COMPOUND SENSATIONS. 219 

CHAPTER XL 

SENSATIONS AND JUDGMENT. 

Section I. — Compound Sensations, 

290. Our Sensations mostly Composite. — In explaining 
the functions of the sensory organs, I have hitherto confined 
myself to describing the means by which the physical agent of a 
sensation is enabled to irritate a given sensory nerve ; and to 
giving some account of the simple sensations which are thus 
evolved. 

Simple sensations of this kind are such as might be produced 
by the irritation of a single nerve fibre, or of several nerve 
fibres by the same agent. Such are the sensations of contact, 
of warmth, of sweetness, of an odor, of a musical note, of white- 
ness, or redness. 

But very few of our sensations are thus simple. Most of 
even those which we are in the habit of regarding as simple, 
are really compounds of different sensations, or of sensations 
with ideas, or judgments. For example, in the preceding cases,' 
it is very difficult to separate the sensation of contact from the 
judgment that something is touching us ; of sweetness, from 
the idea of something in the mouth ; of sound or light, from 
the judgment that something outside us is shining, or sounding. 

291. The Sensation of Smell the Simplest.— The sensa- 
tions of smell are those which are least complicated by acces- 
sories of this sort. Thus, particles of musk diftuse themselves 
with great rapidity through the nasal passages, and give rise to 
the sensation of a powerful odor. But beyond a broad notion 
that the odor is in the nose, this sensation is unaccompanied 
by any ideas of locality and direction. Still less does it give 
rise to any conception of form, or size, or force, or of succes- 
sion, or contemporaneity. If a man had no other sense than 
that of smell, and musk were the only odorous body, he could 



220 ELEMENTAEY PHYSIOLOGY. 

have no sense of outness — no power of distinguishing between 
the external world and himself. 

292. Analysis of a Tactile Sensation. — Contrast this with 
what may seem to be the equally simple sensation obtained by 
drawing the finger along the table, the eyes being shut. This 
act gives one the sensation of a flat hard surface outside one- 
self, which appears to be just as simple as the odor of musk, 
but is really a coniplex state of feeling compounded of 

(a) Pure sensations of contact. 

(h) Pure muscular sensations of two kinds — the one arising 
from the resistance of the table, the other from the actions of 
those muscles which draw the finger along. 

(c) Ideas of the order in which these pure sensations succeed 
one another. 

{d) Comparisons of these sensations and their order, with 
the recollection of like sensations similarly arranged, w^hich 
have been obtained oa previous occasions. 

(e) Recollections of the impressions of extension, flatness, 
&c., made in the organ of vision when these previous tactile 
and muscular sensations were obtained. 

Thus, in this case, the only pure sensations are those of 
contact and muscular action. The greater part of what we call 
the sensation is a complex mass of present and recollected ideas 
and judgments. 

293. Complexity of the Notion of Roundness. — Should 
fmy doubt remain that we do thus mix up our sensations with 
our judgments into one indistinguishable whole, shut the eyes 
as before, and instead of touching the table with the finger, 
take a round lead pencil between the fingers, and draw that 
along the table. The ^' sensation " of a flat hard substance will 
be just as clear as before ; and yet all that we touch is the 
round surface of the pencil, and the only pure sensations we 
owe to the table arc those afforded by the muscular sense. In 
fact, in this case, our *' sensation " of a flat hard surface is en- 
tirely a judgment based upon what the muscular sense tells us 
is going on in certain muscles. 



COMPOUND SENSATIONS. 221 

A still more striking case of the tenacity with which we 
adhere to complex judgments, which we conceive to be pure 
sensations, and are unable to analyze otherwise than by a pro- 
cess of abstract reasoning, is afforded by our sense of roundness. 

Any one taking a marble between two fingers will say that 
he feels it to be a single round body ; and he will probably be 
as much at a loss to answer the question how he knows that it 
is round, as he would be if he were asked how he knows that 
a scent is a scent. 

Nevertheless, this notion of the roundness of the marble is 
really a very complex judgment, and that it is so may be shown 
by a very simple experiment. If the index and middle fingers 
be crossed, and the marble placed between them, so as to be in 
contact with both, it is utterly impossible to avoid the belief 
that there are two marbles instead of one. Even looking at 
the marble, and seeing that there is only one, does not weaken 
the apparent proof derived from touch that there are two.^ 

The fact is, that our notions of singleness and roundness are, 
really, highly complex judgments based upon a few simple sen- 
sations; and when the ordinary conditions of those judgments 
are reversed, the judgment is also reversed. 

With the index and middle fingers in their ordinary posi- 
tion, it is of course impossible that the outer sides of each 
should touch opposite surfaces of one spheroidal body. If, in 
the natural and usual position of the fingers, their outer surfaces 
simultaneously give us the impression of a spheroid (which it- 
self is a complex judgment), it is in the nature of things that 
there must be two spheroids. But when the fingers are crossed 
over the marble, the outer side of each finger is really in con- 
tact wdth a spheroid; and the mind, taking no cognizance of 
the crossing, judges in accordance with its universal expe- 
rience that two spheroids, and not one, give rise to the sensa- 
tions which are perceived. 

* A ludicrous form of this cxpcrimeut is to apply the crossed fingers to the end 
of the nose, when it at once appears double ; and, in spite of the absurdity of the con- 
viction, the mind cannot expel it, so long as the sensations last. 



222 ELEMENTARY PHYSIOLOGY. 



Section II. — Delusions of Judgment 

294. There are no " Delusions of the Senses." — Phenom- 
ena of this kind are not uncommonly called delusions of the 
senses ; but there is no such thing as a fictitious, or delusive, 
sensation. A sensation must exist to be a sensation, and if it 
exists it is real and not delusive. But the judgments we form 
respecting the causes and conditions of the sensations of which 
we are aware, are very often erroneous and delusive enough ; 
and such judgments may be brought about in the domain of 
every sense, either by artificially contrived combinations of 
sensations, or by the inflaence of unusual conditions of the 
body itself. The latter give rise to what are called subjective 
sensations. 

Mankind would be subject to fewer delusions than they 
are, if they constantly bore in mind their liability to false 
judgments, due to unusual combinations, either artificial or 
natural, of true sensations. Men say, " I felt," " I heard," " I 
saw " such and such a thing, when, in ninety-nine cases out of 
a hundred, what they really mean is, that they judge that cer- 
tain sensations of touch, hearing, or sight, of which they were 
conscious, were caused by such and such things. 

295. Subjective Sensations. — Among subjective sensations 
within the domain of touch are the feelings of creeping and 
prickling of the skin which are not uncommon in certain states 
of the circulation. The subjective evil smells and bad tastes 
which accompany some diseases are very probably due to 
similar disturbances in the circulation of the sensory organs of 
smell and taste. 

Many persons are liable to what may be called auditory 
spectra — ^music of various degrees of complexity sounding in 
their ears, without any external cause, while they are wide 
awake. I know not if other persons are similarly troubled, 
but in reading books written by persons with whom I am ac- 
quainted, I am sometimes tormented by hearing the words 



DELUSIONS OF JUDGMENT. 223 

pronounced in the exact way in which these persons would 
utter them, any trick or peculiarity of voice, or gesture, being, 
also, very accurately reproduced. And I suppose that every 
one must have been startled, at times, by the extreme distinct- 
ness with which his thoughts have embodied themselves in ap- 
parent voices. 

The most wonderful exemplifications of subjective sensa- 
tion, however, are afforded by the organ of sight. 

Any one who has witnessed the sufferings of a man labor- 
ing under delirium tremens (a disease produced by excessive 
drinking), from the marvellous distinctness of his visions, which 
sometimes take the form of devils, sometimes of creeping ani- 
mals, but almost always of something fearful or loathsome, will 
not doubt the intensity of subjective sensations in the domain 
of vision. 

298. Remarkable Case of Delusive Appearances.— But 
that illusive visions of great distinctness should appear, it is 
not necessary for the nervous system to be thus obviously de- 
ranged. People in the full possession of their faculties, and of 
high intelligence, may be subject to such appearances, for 
which no distinct cause can be assigned. The best illustration 
of this is the famous case of Mrs. A. given by Sir David 
Brewster, in his " Natural Magic," the chief points of which I 
proceed to quote : 

"(1) The first illusion to which Mrs. A. was subject, was 
one which affected only the ear. On the 21st of December, 
1830, about half-past four in the afternoon, she was standing 
near the fire in the hall, and on the point of going up to dress, 
when she heard, as she supposed, her husband's voice calling 

her by name. ' , , come here ! come to me ! ' She 

imagined that he was calling at the door to have it opened ; 
but upon going there and opening the door, she was surprised 
to find no person there. Upon returning to the fire she again 
heard the same voice calling out very distinctly and loudly, 

* , come, come here ! ' . She then opened two other doors 

of the same room, and upon seeing no person, she returned to 



224 ELEMENTARY PHYSIOLOGY. 

the fireplace. After a few moments she heard the same voice 
still calling, ^ Come to me, come! come away!' in a loud, 
plaintive, and somewhat impatient tone; she answered as 
loudly, ^ Where are you? I don't know where you are,' still 
imagining that he was somewhere in search of her; but re- 
ceiving no answer, she shortly went up-stairs. On Mr. A.'s 
return to the house, about half an hour afterward, she inquired 
why he called to her so often, and where he was, and she was of 
course greatly surprised to learn that he had not been near the 
house at the time. A similar illusion, which excited no par- 
ticular notice at the time, occurred to Mrs. A. when residing at 
Florence, about ten years before, and when she was in perfect 
health. When she was undressing after a ball, she heard a 
voice call her repeatedly by name, and she was at that time 
unable to account for it. 

" (2) The next illusion which occurred to Mrs. A. was of a 
more alarming character. On the 30th of December, about 
four o'clock in the afternoon, Mrs. A. came down-stairs into 
the drawing-room, which she had quitted only a few minutes 
before, and on entering the room she saw her husband, as she 
supposed, standing wdth his back to the fire. As he had gone 
out to take a walk about half an hour before, she was surprised 
to see him there, and asked him why he had returned so soon. 
The figure looked fixedly at her with a serious and thoughtful 
expression of countenance, but did not speak. Supposing that 
his mind was absorbed in thought, she sat down in an arm- 
chair near the fire, and within two feet, at most, of the figure, 
which she still saw standing before her. As its eyes, however, 
still continued to be fixed upon her, she said, after the lapse of 
a few minutes, *Why don't you speak?' The figure imme- 
diately moved off" toward the window at the farther end of 
the room, with its eyes still gazing on her, and it passed so 
very close to her in doing so, that she was struck by the cir- 
cumstance of hearing no step or sound, nor feeling her clothes 
brushed against, nor even any agitation in the air. 

" Although she was now convinced that the figure was not 



DELUSIONS OF JUDGMENT. 225 

her husband, yet she never for a moment supposed that it was 
any thing supernatural, and was soon convinced that it was a 
spectral illusion. As soon as this conviction had established 
itself in her mind, she recollected the experiment which I had 
suggested of trying to double the object ; but before she v^as 
able distinctly to do this, the figure had retreated to the win- 
dow, where it disappeared. Mrs. A. immediately followed it, 
shook the curtains, and examined the window, the impression 
having been so distinct and forcible, that she was unwilling to 
believe that it was not a reality. Finding, however, that the 
figure had no natural means of escape, she was convinced that 
she had seen a spectral apparition like that recorded in Dr. 
Hibbert's work, and she consequently felt no alarm or agita- 
tion. The appearance was seen in bright daylight, and lasted 
four or ^ye minutes. When the figure stood close to her, it 
concealed the real objects behind it, and the apparition was 
fully as vivid as the reality. 

" (3) On these two occasions Mrs. A. was alone, but when 
the next phantom appeared, her husband was present. This 
took place on the 4th of January, 1830. About ten o'clock 
at night, when Mr. and Mrs. A. were sitting in the drawino-- 
room, Mr. A. took up the poker to stir the fire, and when he 
was in the act of doing this, Mrs. A. exclaimed, ' Why, there's 
the cat in the room ! ' ' Where ? ' exclaimed Mr. A. ' There, 
close to you,' she replied. ' Where ? ' he repeated. * Why, 
on the rug to be sure, between yourself and the coal-scuttle.' 
Mr. A., who had still the poker in his hand, pushed it in the 
direction mentioned. ' Take care,' cried Mrs. A., ' take care ! 
you are hitting her with the poker.' Mr. A. again asked her 
to point out exactly where she saw^ the cat. She replied, 
'Why, sitting up there close to your feet on the rug; she is 
looking at me. It is Kitty — come here, Kitty ! ' There were 
two cats in the house, one of which went by this name, and 
they were rarely, if ever, in the drawing-room. 

"At this time Mrs. A. had no idea that the sight of the cat 
was an illusion. When she was asked to touch it, she got up 
10^' 



226 ELEMENTARY PHYSIOLOGY. 

for tlie purpose, and seemed as if she were pursuing something 
which moved away. She followed a few steps, and then said, 
' It has gone under the chair.' Mr. A. assured her that it was 
an illusion, but she would not beheve it. He then lifted up 
the chair, and Mrs. A. saw nothing more of it. The room was 
searched all over, and nothing found in it. There was a dog 
lying on the hearth, who would have betrayed great uneasiness 
if a cat had been in the room, but he lay perfectly quiet. In 
order to be quite certain, Mr. A. rang the bell, and sent for the 
cats, both of which were found in the housekeeper's room. 

" (4) About a month after this occurrence, Mrs. A., who 
had taken a somewhat fatiguing drive during the day, was 
preparing to go to bed about eleven o'clock at night, and, sit- 
ting before the dressing-glass, was occupied in arranging her 
hair. She was in a listless and drowsy state of mind, but fully 
awake. When her fingers were in active motion among the 
papillotes, she was suddenly startled by seeing in the mirror 
the figure of a near relative, who was then in Scotland, and in 
perfect health. The apparition appeared over her left shoulder, 
and its eyes met hers in the glass. It was enveloped in grave- 
clothes, closely pinned, as is usual with corpses, round the 
head and under the chin ; and though the eyes were open, the 
features were solemn and rigid. The dress was evidently a 
shroud, as Mrs. A. remarked -even the punctured pattern usu- 
ally worked in a peculiar manner round the edges of that gar- 
ment. Mrs. A. described herself as, at the time, sensible of a 
feehng, like what we conceive of fascination, compelling her, 
for a time, to gaze upon this melancholy apparition, which was 
as distinct and vivid as any reflected reality could be, the light 
of the candle upon the dressing-table appearing to shine fully 
upon its face. After a few minutes she turned round to look 
for the reality of the fonn over her shoulder, but it was not 
visible, and it had also disappeared from the glass when she 
looked ao;ain in that direction. 

«r * * * * 

" (7) On the llth March, Mrs. A. was preparing for bed. 



DELUSIONS OF JUDGMENT. 227 

Slie had dismissed her maid, and was sitting with her feet in 
hot water. Having an excellent memory, she had been think- 
ing upon and repeating to herself a striking passage in the 
Edinburgh Review^ when, on raising her eyes, she saw seated 
in a large feasy- chair before her the figure of a deceased friend, 
the sister of Mr. A. The figure was dressed, as had been 
usual with her, with great neatness, but in a gown of a peculiar 
kind, such as Mrs. A. had never seen her wear, but exactly such 
as had been described to her by a common friend as having 
been worn by Mr. A.'s sister during her last visit to England. 
Mrs. A. paid particular attention to the dress, air, and appear- 
ance of the figure, w^hich sat in an easy attitude in the chair, 
holding a handkerchief in one hand. Mrs. A, tried to speak 
to it, but experienced a difficulty in doing so, and in about 
three minutes the figure disappeared. 

"About a minute afterward, Mr. A. came into the room, 
and found Mrs. A. slightly nervous, but fully aware of the de- 
lusive nature of the apparition. She described it as having all 
the vivid coloring and apparent reality of life ; and for some 
hours preceding this and other visions she experienced a pecu- 
liar sensation in her eyes, which seemed to be relieved when 

the vision had ceased. 

jft * * * * 

"(9) On the 11th October, when sitting in the drawing- 
room, on one side of the fireplace, she saw the figure of an- 
other deceased friend moving toward her from the window- at 
the farther end of the room. It approached the fireplace, and 
sat down in the chair opposite. As there were several persons 
in the room at the time, she describes the idea uppermost in 
her mind to have been a fear lest they should be alanncd at 
her staring, in the way she was conscious of doing, at vacancy, 
and should fancy her intellect disordered. Under the influence 
of this fear, and recollecting a story of a similar effect in your * 
work on demonology, which she had lately read, she summoned 

* Sir Walter Scott; to whom Sir David Brewster's letters on natural mngic were 
addressed. 



228 ELEMENTARY PHYSIOLOGY. 

up the requisite resolution to enable her to cross the space be- 
fore the firephice, and seat herself in the sanae chair with the 
figure. The apparition remained perfectly distinct till she sat 
down, as it w ere, in its lap, when it vanished." 

297. Personal Characteristics. — It should be mentioned 
that Mrs. A. was naturally a person of very vivid imagination, 
and that, at the time the most notable of these illusions ap- 
peared, her health was weak from bronchitis and enfeebled di- 
gestion. 

It is obvious that nothing but the singular courage and 
clear intellect of Mrs. A. prevented her from becoming a mine 
of ghost-stories of the most excellently authenticated kind. 
And the particular value of her history lies in its showing, that 
the clearest testimony of the most unimpeachable witness may 
be quite inconclusive as to the objective reality of something 
w^hich the witness has seen. 

298. The Senses not at Fault. — Mrs. A. undoubtedly saw 
what she said she saw. The evidence of her eyes as to the ex- 
istence of the apparitions, and of her ears to those of the voices, 
was, in itself, as perfectly trustworthy as their evidence w^ould 
have been had the objects really existed. For there can be no 
doubt that exactly those parts of her retina, which would have 
been affected by the image of a cat, and those parts of her 
auditory organ, which would have been set vibrating by her 
husband's voice, were thrown into the same condition by some 
internal cause. 

What the senses testify is neither more nor less than the 
fact of their own afiection. As to the cause of that affec- 
tion they really say nothing, but leave the mind to form its 
own judgment on the matter. A hasty or superstitious per- 
son in Mrs. A.'s place would have formed a wrong judgment, 
and would have stood by it on the plea that " she must believe 
her senses." ^ 

299. Ventriloquism. — The delusions of the judgment, pro- 
duced not by abnormal conditions of the body, but by unusual 
or artificial combinations of sensations, or by suggjestions of 



DELUSIONS OF JUDGMENT. 229 

ideas, are exceedingly numerous, and, occasionally, are not a 
little remarkable. 

Some of those which arise out of the sensation of touch have 
already been noted. I do not know of any produced through 
smell or taste, but hearing is a fertile source of such errors. 

What is called Ventriloquism (speaking from the belly), 
and is not uncommonly ascribed to a mysterious power of 
producing voice somewhere else than in the larynx, depends 
entirely upon the accuracy with which the performer can 
simulate sounds of a particular character, and upon the skill 
with which he can suggest a belief in the existence of the 
causes of these sounds. Thus, if the ventriloquist desire to 
create the belief that a voice issues from the bowels of the 
earth, he imitates with great accuracy the tones of such a half- 
stifled voice, and suggests the existence of some one uttering 
it by directing his answers and gestures toward the ground. 
These gestures and tones are such as would be produced by a 
given cause; and no other cause being apparent, the mind of 
the bystander insensibly judges the suggested cause to exist. 

Section III. — Visual Sensations and Mental States, 

300. Optical Delusions. — The delusions of the judgment 
through the sense of sight, optical delusions, as they are called, 
are more numerous than any others, because such a great 
number of what we think to be simple visual sensations, are 
really very complex aggregates of visual sensations, tactile sen- 
sations, judgments, and recollections of former sensations and 
judgments. 

It will be instructive to analyze some of these judgments 
into their principles, and to explain the delusions by the appli- 
cation of these principles. 

301. Externality of Visible Objects. — JJlien an external 
body is felt by the touch to be in a given place, the image of that 
body falls on a point of the retina, which lies at one end of a 
straight line joining the body and the retina, and traversing a 



230 ELEMENTARY PHYSIOLOGY. 

particular region of the centre of the eye. This straight line is 
called the optic axis. 

Conversely, when any part of the surface of the retina is ex- 
cited, the luminous sensation is referred hy the mind to some 
point outside the body, in the direction of the optic axis. 

It is for this reason tliat when a phosphene is created by- 
pressure, say on the outer and lower side of the eyeball, the 
luminous image appears to lie above, and to the inner side of 
the eye. Any external object which could produce the sense 
of light in the part of the retina pressed upon, must, in fact, 
occupy this position ; and hence the mind refers the light seen 
to an object in that position. 

302. The Inversion of the Visual Images. — The same 
kind of explanation is applicable to the apparent paradox that, 
while all the pictures of external objects are certainly inverted 
on the retina by the refracting media of the eye, Ave neverthe- 
less see them upright. It is difficult to understand this, until 
one reflects that the retina has, in itself, no means of indicating 
to the mind which of its parts lies at the top, and which at the 
bottom ; and that the mind learns to call an impression on the 
retina high or low, right or left, simply on account of the asso- 
ciation of such an impression with certain coincident tactile 
impressions. In other words, when one part of the retina is 
affected, the object causing the affection is found to be near 
the right hand; when another, the left; when another, the 
hand has to be raised to reach the object; when yet another, 
it has to be depressed to reach it. And thus the several im- 
pressions on the retina are called right, left; upper, lower, quite 
irrespectively of their real positions, of which the mmd has, 
and can have, no cognizance. 

303. Correspondence of Objects and Images. — When an 
external body is ascertained by touch to be single, it forms but 
one image on the retina of a single eye ; and when two or more 
images fall on the retina of a single eye, they ordinarily proceed 
from a corresponding number cf bodies which are distinct to the 
touch. 



VISUAL SENSATIONS AND MENTAL STATES. 231 

Conversely^ the sensation of two or more images is judged hy 
the mind to proceed from two or more objects. 

If two pin-holes be made in a piece of cardboard at a dis- 
tance less than the diameter of the pupil, and a small object 
like the head of a pin be held pretty close to the eye, and 
viewed through these holes, two images of the head of the pin 
will be seen. The reason of this is, that the rays of light from 
the head of the pin are split by the card into two minute pen- 
cils, which pass into the eye on either side of its centre, and 
cannot be brought to one focus on account of the nearness of 
the pin to the eye. Hence they fall on different parts of the 
retina, and each pencil being very small, makes a tolerably 
distinct image of its own on the retina. Each of these images 
is now referred outward (p. 229) in the direction of the appro- 
priate optic axis, and two pins are apparently seen instead of 
one. A like explanation applies to multiplying glasses and 
doubly refracting crystals, both of which, in their own ways, 
split the pencils of light proceeding from a single object into 
two or more separate bundles. These give rise to as many 
images, each of which is referred by the mind to a distinct ex- 
ternal object. 

304. Judgment of Distance— Perspective. — Certain visual 
phenomena ordinai'ily accompany those products of tactile sen- 
sation to which we give the name of size, distance, and form. 
Thus, other things being alike, the space of the retina, covered by 
the image of a large object, is larger than that covered by a 
small object ; while that covered by a near object is larger than 
that covered by a distant object ; and, other conditions being 
alike^ a near object is more brilliant than a distant one. Fur- 
thermore, the shadows of objects differ with the forms of their 
surfaces, as determined by touch. 

Conversely, if these visual phenomena can be produced, they 
inevitably suggest a belief in the existence of objects co^npcfent to 
produce the corres2Jonding tactile sensations. 

What is Q,di\\Q^ perspective, whether solid, or aerial, in draw- 
ing or painting, depends on the application of these principles. 



232 ELEMENTARY PHYSIOLOGY. 

It is a kind of visual ventriloquism — the painter putting upon 
his canvas all the conditions requisite for the production of 
images on the retina, having the form, relative size, and inten- 
sity of color, of those which would actually be produced by 
the objects themselves in nature. And the success of his pic- 
ture, as an imitation, depends upon the closeness of the resem- 
blance between the images it produces on the retina, and those 
which would be produced by the objects represented. 

305. Magnifying Glasses. — To most persons the image of 
a pin, at five or six inches from the eye, appears blurred and 
indistinct— the eye not being capable of adjustment to so short 
a focus. If a small hole be made in a piece of card, the cir- 
cumferential rays which cause the blur are cut off and the 
image becomes distinct. But at the same time it is magnified, 
or looks bigger, because the image of the pin occupies a much 
larger extent of the retina when close than when distant. All 
convex glasses produce the same effect — while concave lenses 
diminish the apparent size of an object, because they diminish 
the size of its image on the retina. 

308. Why the Sun and Moon look larger near the 
Horizon. — The moon, or the sun, when near the horizon ap- 
pear very much larger than they are Avhen high in the sky. 
When in the latter position, in fact, we have nothing to com- 
pare them with, and the small extent of the retina which their 
images occupy suggests small absolute size. But, as they set, 
we see them passing behind great trees and buildings which 
we know to be very large and very distant, and yet occupying 
a larger space on the retina than the latter do. Hence the 
vague suggestion of their larger size. 

307. Judgment of Form by Shadows. — If a convex sur- 
face be lighted from one side, the side toward the light is 
bright — that turned from the light, dark, or in shadow — while 
a concavity is shaded on the side toward the light, bright on 
the opposite side. 

If a new half-crown, or a medal with a well-raised head 
upon its face, be lighted sideways by a candle, we at once know 



VISUAL SENSATIONS AND MENTAL STATES. 233 

the head to be raised (or a cameo) by the disposition of the 
light and shade ; and if an intaglio^ or medal on which the 
head is hollowed out be Hghted in the same way, its nature is 
as readily judged by the eye. 

But now, if either of the objects thus lighted be viewed 
with a convex lens, which inverts its position, the light and 
dark sides will be reversed. With the reversal the judgment 
of the mind will change, so that the cameo will be regarded as 
an intaglio, and the intaglio as a cameo; for the light still 
comes from where it did, but the cameo appears to have the 
shadows of an intaglio, and vice versa. So completely, how- 
ever, is this interpretation of the facts a matter of judgment, 
that if a pin be stuck beside the medal so as to throw a shadow, 
the pin audits shadow, being reversed by the lens, will suggest 
that the direction of the light is also reversed, and the medals 
will seem to be what they really are. 

308. Judgment of Changes of Form. — Whenever an ex- 
ternal object is watched rapidly changing its form ^ a continuous 
series of different pictures of the object is impressed upon the 
same spot of the retina. 

Conversely J if a continuous series of different pictures of one 
object is impressed upon one part of the retina, the mind judges 
that they are due to a single external object, undergoing changes 
of form. 

This is the principle of the curious toy called the thauma- 
trope, by the help of which, on looking through a hole, one 
sees images of jugglers throwing up and catching balls, or boys 
playing at leap-frog over one another's backs. This is man- 
aged by painting at intervals, on a disk of card, fignires and 
jugglers in the attitudes of throwing, waiting to catch, and 
catching ; or boys " giving a back," leaping, and coming into 
position after leaping. The disk is then made to rotate before 
an opening, so that each image shall be presented for an in- 
stant, and follow its predecessor before the impression of the 
latter has died away. The result is, that the succession of dif- 
ferent pictures irresistibly suggests one or more objects under- 



234 ELEMENTARY PHYSIOLOGY. 

going successive changes- — the juggler seems to throw the balls, 
and the boys appear to jump over one another's backs. 

309. Single Vision with Two Eyes. — When an external 
object is ascertained hy touch to he single^ the centres of its reti- 
nal images in the two eyes fall upon the centres of the yellow 
spots of the two eyes^ when both eyes are directed toward it ; 
but if there be two external objects^ the centres of both their 
images cannot fall ^ at the same timCj upon the centres of the yel- 
low spots. 

Conversely^ tvhen the centimes of two images^ formed simul- 
taneously in the two eyes, fall upon the centres of the yellow 
spots, the mind judges the images to be caused by a single exter- 
nal object : but if not, by two. 

This seems to be the only admissible explanation of the 
facts, that an object which appears single to the touch and 
when viewed with one eye, also appears single when it is viewed 
with both eyes, though two images of it are necessarily formed; 
and on the other hand, that when the centres of the two im- 
ages of one object do not fall on the centres of the yellow 
spots, both images are seen separately, and we have double 
vision. In squinting, the axes of the two eyes do not converge 
equally toward the object viewed. In consequence of this, 
when the centre of the image formed by one eye falls on the 
yellow spot, the corresponding part of that formed by the other 
eye does not, and double vision is the result. 

310. The Pseudoscope. — In single vision with two eyes, the 
axes of the tioo eyes, of the movements of which the muscular 
sense gives an indication, cut one another at a greater angle 
ivhen the object approaches, at a less angle when it goes farther 
off. 

Conversely, if without changing the position of an object, the 
axes of the two eyess, which view it can be made to converge or 
diverge, the object will seem to approach or go farther off. 

In the instrument called the pseudoscope, mirrors or prisms 
are disposed in such a manner that the rays of light from a 
stationary object can be caused to alter the angle at which 



VISUAL SENSATIONS AND MENTAL STATES. 235 

they enter the two eyes, and so require the axes of these eyes 
to become more or less convergent. In the former case the 
object seems to approach ; in the latter, to increase its dis- 
tance. 

311. Judgment of Solidity— the Stereoscope. — When a 
body of moderate size, ascertained by touch to be solid, is viewed 
with both eyes, the images of it, formed by the two eyes, are 
necessarily different (one showing more of its right side, the other 
of its left side). Nevertheless, they coalesce into a common 
image, which gives the impression of solidity. 

Conversely, if the two images of the right and left aspects 
of a solid body be made to fall upon the retince of the two eyes 
in such a way as to coalesce into a common image^ they are 
judged by the mind to proceed from the single solid body which 
alone, under ordinary circumstances, is competent to produce them. 

The stereoscope is constructed upon this principle. What- 
ever its form, it is so contrived as to throw the images of two 
pictures of a solid body, such as would be obtained by the 
right and left eye of a spectator, on to such parts of the retinae 
of the person who uses the stereoscope as would receive these 
images, if they really proceeded from one solid body. The 
mind immediately judges them to arise from a single external 
solid body, and sees such a solid body in place of the two 
pictures. 

The operation of the mind upon the sensations presented to 
it by the two eyes is exactly comparable to that which takes 
place when, on holding a marble between the finger and thumb, 
we at once declare it to be a single sphere (p. 221). That 
which is absolutely presented to the mind by the sense of touch 
in this case is by no means the sensation of one spheroidal 
body, but two distinct sensations of two convex surfaces. That 
these two distinct convexities belong to one sphere, is an act of 
judgment, or process of unconscious reasoning, based upon 
many particulars of past and present experience, of which we 
have at the moment no distinct consciousness. 



236 ELEMENTARY PHYSIOLOGY. 



CHAPTER XIL 

THE NEEYOUS SYSTEM AND INNEEYATION. 

Section I. — The Spinal Cord — Reflex Actions, 

312. The General Nervous System. — The sensory organs 
are, as we Lave seen, the channels through "which particular 
physical agents are enabled to excite the sensory nerves with 
which these organs are connected ; and the activity of these 
nerves is evidenced by that of the central or^-an of the nervous 
system, which becomes manifest as a state of consciousness — 
the sensation. 

We have also seen that the muscles are instruments by 
which a motor nerve, excited by the central organ with which 
it is connected, is able to produce motion. 

The sensory nerves, the motor nerves, and the central organ, 
constitute the greater part of the nervous system, which, with 
its function of innervation, we must now study somewhat more 
closely, and as a whole. 

313. The Cerebro-Spinal and Sympathetic Systems. — 
The nervous apparatus consists of two sets of nerves and nerve 
centres, which are intimately connected together, and yet may 
be conveniently studied apart. These are the cerebrospinal 
system and the sympathetic system. The former consists of the 
cerebrospinal axis (composed of the brain and spinal cord) and 
the cerebral and spinal nerves, which are connected with this 
axis. The latter comprises the chain of sympathetic ganglia y 
the nerves which they give off, and the nervous cords by which 
they are connected with one another and with the cerebro- 
spinal nerves. 

314. Membrane of the Cerebro-Spinal Axis. — The cere- 
bi'O'Spinal axis lies in the cavity of the skull and spinal column, 
the bony walls of which cavity are lined by a very tough fibrous 



THE SPINAL CORD — REFLEX ACTIONS. 237 

membrane, serving as the periosteum of the component bones 
of this region, and called the dura mater. The brain and spinal 
cord themselves are closely invested by a very vascular fibrous 
tissue, called J9ia mater ^ which is continued, more or less exten- 
sively, into the substance of these organs along with the ves- 
sels. The outer surface of the pia mater ^ and the inner sur- 
face of the dura mater ^ pass into a delicate fibrous tissue, lined 
by an epithelium, which is called the arachnoid membrane. 
Thus one layer of arachnoid coats the brain and spinal cord, 
and another lines the dura mater. As these layers become 
continuous with one another at various points, the arachnoid 
forms a sort of shut sac, like the pericardium ; and, in com- 
mon with other serous membranes, it secretes a fluid, the 
arachnoid fluid ^ into its interior. The interspace between the 
internal and external layers of the arachnoid of the brain is, for 
the most part, very small ; that between the corresponding 
layers of the arachnoid of the spinal cord is larger. 

315. The Spinal Cord.— The spinal cord (Fig. 89) is a 
column of grayish- white soft substance, extending from the top 
of the spinal canal, where it is continuous with the brain, to 
about the second lumbar vertebra, where it tapers off to a point. 
A deep fissure, the anterior fissure^ divides it in the middle 
line in front, nearly down to its centre; and a similar fissure, 
the posterior fissure, also extends nearly to its centre in the 
middle line behind. The pia mater extends into each of these 
fissures, and supports the vessels which supply the cord with 
its blood. In consequence of the presence of these tissues, 
only a narrow bridge of the substance of the cord connects its 
two halves, and this bridge is traversed throughout its entire 
length by a minute canal, the central canal of the cord. 

Each half of the cord is divided longitudinallv into three 
equal parts, by the lines of attachment of two parallel series of 
dehcate bundles of nervous filaments, the roots of the spinal 
nerves. The roots of the nerves which arise along that line 
which is nearer the posterior surface of the cord are called jpos- 
terior roots ; those which arise along the other line are the an- 



238 



ELEMENTARY PHYSIOLOGY. 



terior roots, A certain number of anterior and posterior roots, 
on the same level on each side of the cord, converge and form 
anterior and posterior bundles, and then the two bundles, ante- 
rior and posterior, coalesce into the trunk of a spinal nerve ; 
but, before doing so, the posterior bundle presents an enlarge- 
ment — the ganglion of the posterior root. 

The trunks of the spinal nerves pass out of the spinal canal 
by the intervertebral foramina^ or apertures between the verte- 
brae, and then divide and subdivide, their ultimate ramifica- 
tions going to the muscles and to the skin. 

There are thirty-one pairs of these spinal nerves, and, con- 
sequently, twice as many sets of roots of spinal nerves given 
off, in two lateral series, from each half of the cord. 




Fig. 89. 



Fig. 90. 



The spinal cord. — Fig:. 89, a front view of a portion of the cord. On the left side, the 
anterior roots, A.B.^ are entire ; on the right side they are cut, to show the pos- 
terior roots, P.R. 

Fig. 90, a transverse section of the cord. A. the anterior fissure; P, the posterior 
fissure ; G. the central canal ; C. the gray matter ; W. the white matter. A.R. 
the anterior root, P,B. the posterior root, €hn. the ganglion, and 71 the trunk, 
of a spinal nerve. 



316. Transverse Section of the Cord. — A transverse sec- 
tion of the cord (Fig. 90) shows that each half contains two 
substances — a white substance on the outside, and a grayish-red 
substance in the interior. And this gray substance is so dis- 
posed that, in transverse section, it looks something like a 
crescent, with one end bigger than the other, and with the 
concave side turned outward. The two ends of the crescent 
are called its horns or cornua, the one in front being the ante- 
rior cornu ; the one turned backward the posterior cornu. The 
convex sides of the cornua of the two halves approach one an- 



THE SPINAL CORD REFLEX ACTIONS. 239 

other, and are joined by the bridge which contains the central 
canal. 

Many of the nerve fibres of which the anterior roots are 
composed may be traced into the anterior corn a, while those 
of the posterior roots enter the posterior comu. 

317. Physiological Properties of Nerves. — The physio- 
logical properties of the organs now described are very remark- 
able. 

If the trunk of a spinal nerve be irritated in any way, as by 
pinching, cutting, galvanizing, or applying a hot body, two 
things happen : in the first place, all the muscles to which fila- 
ments of this nerve are distributed, contract ; in the second, 
acute pain is felt, and the pain is refeiTcd to that part of the 
skin to which fibres of the nerve are distributed. In other 
words, the efi*ect of irritating the trunk of a nerve is the same 
as that of irritating its component fibres at their terminations. 

The eflects just described will follow upon irritation of any 
part of the branches of the nerve ; except that when a branch 
is irritated, the only muscles directly afifected, and the only 
part of the skin to which pain is referred, will be those to which 
that branch sends nerve fibres. And these effects will follow 
upon irritation of any part of the trunk of a nerve up to the 
point at which the anterior and posterior bundles unite. 

318. Functions of Anterior and Posterior Roots. — If the 
anterior bundle of root fibres be irritated in the same way, 
only half the previous effects are brought about. That is to 
say, all the muscles to which the nerve is distributed contract, 
but no pain is felt. 

So again, if the posterior, ganglionated, bundle be irritated, 
only half the effbct of irritating the whole trunk is produced. 
But it is the other half; that is to say, none of the muscles to 
which the nerve is distributed contract, but intense pain is re- 
ferred to the whole area of skin to which the fibres of the nerve 
are distributed. 

It is clear enough, from these experiments, that all the 
power of causing muscular contraction which a spinal nerve 



240 ELEMENTARY PHYSIOLOGY. 

possesses, is lodged in the fibres whicli compose it?, anterior 
roots ; and all the power of giving rise to sensation, in those 
of its posterior roots. Hence the anterior roots are commonly 
called motor ^ and the posterior sensory. 

319. Experiment— Paralysis. — The same truth may be 
ilhistrated in other ways. Thus, if, in a living animal, the an- 
terior roots of a spinal nerve be cut, the animal loses all con- 
trol over the muscles to which that nerve is distributed, though 
the sensibility of the region of the skin supplied by the nerve 
is perfect. If the posterior roots be cut, sensation is lost, and 
voluntary movement remains. But, if both roots be cut, neither 
voluntary movement nor sensibility are any longer possessed by 
the part supplied by the nerve. The muscles are said to be 
paralyzed^ and the skin may be cut, or burnt, without any sen- 
sation being excited. 

If, when both roots are cut, that end of the motor root 
which remains connected with the trunk of the nerve be irri- 
tated, the muscles contract; while, if the other end be so 
treated, no apparent effect results. On the other hand, if the 
end of the sensory root connected with the trunk be irritated, 
no apparent effect is produced, while, if the end connected with 
the cord be thus served, violent pain immediately follows. 

When no apparent effect follows upon the irritation of any 
nerve, it is not probable that the molecules of the nerve re- 
main unchanged. On the contrary, it w^ould appear that the 
same change occurs in all cases; but a motor nerve is con- 
nected with nothing that can make that change apparent save a 
muscle ; and a sensory nerve with nothing that can show an 
effect but the central nervous system. 

320. Molecular Changes in Irritated Nerves. — It will be 
observed that in all the experiments mentioned there is evidence 
that, when a nerve is irritated, a something, probably a change 
in the arrangement of its molecules, is propagated along the 
nerve fibres. If a motor or a sensory nerve be irritated, at any 
point, contraction in the muscle, or sensation in the central 
organ, immediately follows. But if the nerve be cut, or even 



THE SPINAL CORD REFLEX ACTIONS. 241 

tightly tied at any point between the part irritated and the 
muscle or central organ, the effect at once ceases, just as cut- 
ting a telegraph-wire stops the transmission of the electric cur- 
rent or impulse. When a limb, as we sa}^, " goes to sleep," it 
is because the nerves supplying it have been subjected to pres- 
sure sufficient to destroy the nervous * continuity of the fibres. 
We lose voluntary control over, and sensation in, the limb, and 
these powers are only gradually restored as that nervous con- 
tinuity returns. 

Having arrived at this notion of an impulse travelling 
along a nerve, we readily pass to the conception of a sensory 
nerve as a nerve which, when active, brings an impulse to the 
central organ, or is afferent ; and of a motor nerve, as a nerve 
which carries away an impulse from the organ, or is efferent It 
is very convenient to use these terms to denote the two great 
classes of nerves ; for, as we shall find, there are afferent nerves 
which are not sensory, while there may be in man, and cer- 
tainly are in animals, efferent nerves which are not motor, in 
the sense of inducing muscular contraction. 

321. The Negative Deflection. — There is no difference in 
structure, in chemical or in physical character, between affer- 
ent and efferent nerves. The impulse which travels along them 
requires a certain time for its propagation, and is vastly slower 
than many other forces — even slower than sound. 

It is found that, during life, the trunk of a nerve is in a 
state of electrical activity, the ends of any segment being in a 
different polar condition to its surflice. Hence, if one pole 
of a galvanometer be connected with the cut end of a nerve, 
and the other with its surface, a current passes, and the needle 
is deflected to a certain extent — say 20 degrees. If, under 



♦Their "nt'rvous continuity" — ^because their physical continuity is not inter- 
rupted as a Avhole, but only that of the substance which acts as a conductor of the 
nervous influence; or, it may be that only the conducting power of a p:irt of that 
substance is interfered with. Imagine a telegraph cable, made of delicate caoutchouc 
tubes, filled with mercury— a squeeze would interrupt the "electrical continuity" of 
the cable, without destroying its physical continuity. This analogy may not be ex- 
act, but it helps to make the nervous phenomena intelligible. 
11 



242 ELEMENTARY PHYSIOLOGY. 

these circumstances, the nerve be irritated (the result of which, 
of course, is the propagation of an impulse along its molecules), 
the deviation of the needle at once diminishes, falling, say, to 
15 degrees. 

This is called negative deflection^ and the importance of the 
experiment consists in the demonstration which it affords of 
the existence of a close relation between the force proper to 
nervous matter and one of the ordinary forces of nature, elec- 
tricity — though this close relation must by no means be mis- 
taken for identity. 

322, Properties of the Spinal Cord. — Up to this point our 
experiments have been confined to the nerves. We may now 
test the properties of the spinal cord in a similar way. If the 
cord be cut across (say in the middle of the bach), the legs and 
all the parts supplied by nerves which come off below the sec- 
tion, will be insensible and incapable of movement by any ef- 
fort of the will ; while all the parts above the section will retain 
their ordinary powers. 

When a man hurts his back by an accident, the cord is not 
unfrequently so damaged as to be virtually cut in two, and then 
paralysis and insensibility of the lower part of the body ensue. 

If, when the cord is cut across in an animal, the face of the 
end below the cut, or away from the brain, be irritated, violent 
movements of all the muscles supplied by nerves given off from 
the lower part of the cord take place, but there is no sensa- 
tion. On the other hand, if the posterior root of any nerve 
attached to the part of the cord, which is still connected with 
the brain, be irritated, great pain ensues, but there is no move- 
ment of the muscles of the part below the cut. 

323. Reflex Action through the Spinal Cord.— Thus it 
may be said that, in relation to the brain, the cord is a great 
mixed motor and sensory nerve. But it is also much more. 
For if the trunk of a spinal nerve be cut through, so as to 
sever its connection with the cord, an irritation of the skin to 
which the sensory fibres of that nerve are distributed, produces 
neither motor nor sensory effect. 



THE SPINAL CORD REFLEX ACTIONS. 243 

But if the cord be cut through, so as to sever its connec- 
tion with the brain, irritation appHed to the skin of the parts 
below the section, though it gives rise to no sensation, may 
produce violent motion of the parts supplied with motor nerves 
from the segment of the cord below the section. 

Thus, in the case supposed above, of a man whose legs are 
paralyzed and insensible from spinal injury, tickling the soles 
of the feet will cause the legs to kick out convulsive]\\ And, 
as a broad fact, it may be said that, so long as both roots of 
the spinal nerves remain connected with the cord, irritation of 
any afferent nerve is competent to give rise to excitement of 
some, or the whole, of the efferent nerves so connected. 

If the cord be cut across a second time at any distance 
from the first section, the efferent nerves below the second cut 
will no longer be affected by irritation of the afferent nerves 
below the cut — but only of those above the cut. Or, in other 
words, in order that an afferent impulse may be converted into 
an efferent one by the spinal cord, the afferent nerve must be 
in uninterrupted material communication with the efferent 
nerve, by means of the substance of the spinal cord. 

This peculiar power of the cord, by which it is competent 
to convert afferent impulses into efferent ones, is that which 
distinguishes it physiologically, as a central organ, from a 
nerve, and is called rejiex action. It is a power possessed by 
the gray matter, and not by the white substance of the cord. 

324. Distribution of Reflex Effects.— The number of the 
efferent nerves which may be excited by the reflex action of 
the cord, is not regulated by the number of the afferent nerves 
which are stimulated by the irritation which gives rise to the 
reflex action. Nor does a simple excitation of the afferent 
nerve by any means imply a corresponding simplicity in the 
arrangement and succession of the reflected motor impulses. 
Tickling the sole of the foot is a very simple excitation of the 
afferent fibres of its nerves ; but, in order to produce the mus- 
cular actions by which the legs are drawn up, a groat multitude 
of efferent fibres must act in regulated coiiibinntion. In tact, 



244 ELEMENTAEY PHYSIOLOGY. 

in a multitude of cases, a reflex action is to be regarded rather 
as an order given by an afferent nerve to the cord, and executed 
by it, than as a mere rebound of the afferent impulse into the 
first efferent channels open to it. 

325. The Spinal Cord as a Conductor. — Thus the spinal 
cord is, in part, merely a transmitter of impressions to and from 
the brain ; but, in part, it is an independent nervous centre, 
capable of originating combined movements upon the reception 
of the impulse of an afferent nerve. 

Regarding it as a conductor, the question arises, do all 
parts of it conduct all kinds of impressions indifferently ? Or 
are certain kinds of impressions communicated only through 
particular parts of the cord ? 

The following experiments furnish a partial reply to these 
questions : 

If the anterior half of the white matter of the dorsal part 
of the cord be cat through, the will is no longer capable of 
exerting any influence on the muscles which are supplied with 
nerves from the lower segment of the cord. A similar section, 
carried through the posterior half of the white matter in this 
region, has no effect on the transmission of voluntary impulses. 
It is obvious, therefore, that in the dorsal part of the cord, 
nervous impulses from the brain are sent through the anterior 
part of the white matter. 

326. Conduction of the Gray Matter. — The posterior half 
of the white matter may be cut through at one point, and the 
anterior half at a point a little higher up, so that all the white 
fibres shall be divided transversely by the one cut or the other 
without any destruction of the material continuity of the cord, 
or damage to the gray matter. 

When this has been done, irritation of those sensory nerves 
which are connected with parts below the section excites the 
sensation of pain as strongly as ever. Hence it follows, that 
the afferent impulses, which excite pain when they reach the 
brain, pass through, and are conveyed by, the gray matter. 
And it has been found, by experiment, that, so long as even a 



THE SPINAL COED — KEFLEX ACTIONS. 245 

small portion of the gray matter remains entire, these afferent 
impulses are efficiently transmitted. Singularly enough, how- 
ever, irritation of the gray matter itself does not cause pain. 

If one half of the cord, say the right, be cut through, trans- 
versely, down to its very middle, so as to interrupt all con- 
tinuity of both white and gray matter between its upper and 
lower parts, irritation of the skin of the right side of the body, 
below the line of section, will give rise to as much pain as be- 
fore, but all voluntary power will be lost in the muscles of that 
side. Hence it follows, that the channels by which the afferent 
impulses are conveyed must cross over, from the side of the 
cord which they enter to the opposite side ; while the efferent 
impulses, sent down from the brain, must travel along that side 
of the cord by which they pass out. 

If this be true, it is clear that a longitudinal section, taken 
through the exact middle of the cord, will greatly impair, if not 
destroy, the sensibility of both sides of the body below the 
section, but will leave the muscles perfectly under the control 
of the will. And it is found experimentally that such is the 
case. 

Section IL — The Brain* 

327. The Vaso-motor Centres. — Such are the functions of 
the spinal cord, taken as a whole. But particular regions of 
this organ appear to be charged with the special function of 
actino- as centres for those vaso-motor nerves which supply the 
muscles of the vessels and of many of the \iscera. 

For example, the muscles of the w alls of the vessels of the 
ear and of the skin of the head generally, are made to contract, 
as has been already mentioned, by nervous fibres derived, im- 
mediately, from the sympathetic. These fibres, however, do 
not arise from the sympathetic ganglia, but simply pass through 
them on their way from the spinal cord, to the upper dorsal 
region of w^hicli they can all be traced. At least, this is the 
only conclusion to be drawn from the facts, that irritation of 



2i6 



ELEMENTARY PHYSIOLOGY. 



this region of tlie cord produces the same effect as irritation 
of the vaso-motor nerves themselves, and that destruction of 
this part of the cord paralyzes them. 



J3 — 




Fig. 91. 

The base of the brain.— ^. frontal lobe; B. temporal lobe of the cerebral hemispheres; 
C.C. corpus cailosum; Ch. cerebellum ; M. medulla oblongata; P. the pituitary 
body; 1. the olfactory nerve ; II. the optic nerve ; III. IV. VI. the nerves of the 
muscles of the eye; V. the trigeminal nerve; VII. the portio dura; VIII. the 
auditory nerve; IX. the glossopharyngeal; X the pneumogastric ; X/. the spinal 
accessory ; XII. the hypoglossal, or motor nerve of the tongue. The number VI. 
is placed upon the Fo}is Varolii. The crura cerebri are the broad bundles of 
fibres which lie between the third and the fourth nerves on each side. 



The gray matter of the upper part of the cord is therefore 
a vaso-motor centre for the head and face. 

328, Outlines of Anatomy of the Brain. — Tlie brain 
(Fig. 91) is a complex organ, consisting of several parts, the 
hindermost of which, termed medulla oblongata^ passes insen- 



THE BEAIK. 



247 



sibly into the spinal cord, and, in its lower part, has the same 
structure as the spinal cord. 

Above, however, it widens out, and the central canal, 
spreading with it, becomes a broad cavity, which (leaving cer- 
tain anatomical minutiae aside) may be said to be widely open 
above. This cavity is termed the fourth ventricle. Over- 
hanging the fourth ventricle is a great laminated mass, the 
cerebellum (Ch, Figs. 91, 93). On each side, this organ sends 
down several layers of transverse fibres, which sweep across 




Fig. 92. 

A vertical and transverse Gection of the brain, taken just behind the pituitary body, 
P. — ^9y. the Sylvian fissure; G.G. the corpus callosum ; F. the fornix; F. the 
lateral ventricle ; Th. the optic thalamus ; (9/7. the optic nerve; ///.the third 
ventricle; F. the lateral ventricle; F', its descending horn. 



the brain and meet in the middle line of its base, forming a 
kind of bridge (called Pons Varolii^ Fig. 91) in front of the 
medulla oblongata. The longitudinal nerve fibres of the me- 
dulla oblongata pass forward among, and between, these layei-s 
of transverse fibres ; and become visible, in front of the pons, 
as two broad diverging bundles, called crura cerebri (Fig. 91). 
Above the crura cerebri lies a mass of nervous matter raised up 
into four hemispherical elevations, called corpora quadricfcmlna 
(Fig. 93). Between these and the crura cerebri is a narrow 



248 ELEMENTAEY PHYSIOLOGY. 

passage, which leads from the fourth ventricle into what is 
termed the tliird ventricle of the brain (Fig. 92, ///.). The 
third ventricle is a narrow cavity lodged between two 
great masses of nervous matter, called optic thalamic into 
which the crura cerebri pass. The roof of the third ventricle 
is merely membranous; and the peculiar body of unknow^n 
function, ih^ pineal gland^ is connected with it. The floor of 
the third ventricle is produced into a sort of funnel, which ends 
in another anomalous organ, the pituitary lody (Figs. 92, 93). 

The third ventricle is closed, in front, by a thin layer of 
nervous matter ; but, behind this, on each side, there is an 
aperture in the boundary wall of the third ventricle whicli 
leads into a large cavity : this occupies the centre of the cere- 
bral liemisplierej and is called the lateral ventricle (Fig. 92). 
Each hemisphere is enlarged backward, downward, and for- 
ward, into as many lobes ; and the lateral ventricle presents 
corresponding prolongations, or cornua. 

The floor of the lateral ventricle is formed by a mass of 
nervous matter, called the corpus striatum, into which the fibres 
that have traversed the optic thalamus enter (Figs. 92, 93). 

The hemispheres are so large that they overlap all the other 
parts of the brain, and, in the upper view, hide them. Their 
applied faces are separated by a median fissure for the greater 
part of their extent ; but, inferiorly, are joined by a thick mass 
of transverse fibres, the corpus callosum (Figs. 91, 92, C.C). 

The outer surfaces of the hemispheres are marked out into 
convolutions, or gyri, by numerous deep fissures (or sulci), into 
which the pia mater enters. One large and deep fissure w^hich 
separates the anterior from the middle division of the hemi- 
sphere is called the fissure of Sylvius (Fig. 92, Sy,), 

329. Arrangement of the White and Gray Matter. — In 
the medulla oblongata the arrangement of the white and gray 
matter is substantially similar to what it is in the spinal cord ; 
that is to say, the white matter is external, and the gray inter- 
nal. But, in the cerebellum and cerebral hemispheres, the gray 
matter is external and the white internal ; w^hile, in the optic 



THE CEREBRAL NERVES. 249 

thalami and corpora striata, gray matter and white niatter are 
variously intermixed. 

Section III. — The Cerebral Nerves, 

330. Their Distribution. — Nerves are given off from the 
brain in pairs, which succeed one another from before back- 
ward, to the number of twelve (Fig. 93). 

The/rs^ pair, counting from before backward, are the olfac- 
tory nerves, and the second are the optic nerves. The functions 
of these have already been described. 

The third pair are called motores oculi (movers of the eye), 
because they are distributed to all the muscles of the eye ex- 
cept two. 

The nerves of the fourth pair and of the sixth pair supply, 
each, one of the muscles of the eye, on each side ; the fourth 
going to the superior oblique muscle, and the sixth to the ex- 
ternal rectus. Thus the muscles of the eye, small and close 
together as they are, receive their nervous stimulus by three 
distinct nerves. 

Each nerve of the fifth pair is very large. It has two roots, 
a motor and a sensory, and further resembles a spinal nerve in 
having a ganglion on its sensory root. It is the nerve which 
supplies the skin of the face and the muscles of the jaw^s, and, 
having three chief divisions, is often called trigeminaL 

The seventh pair furnish with motor nerves the muscles of 
the face, and some other muscles, and are called /aaaZ. 

The eighth pair are the auditory nerves. As the seventh 
and eighth pairs of nerves leave the cavity of the skull together, 
they are often, and especially by English writers on anatomy, 
reckoned as one, divided into portio dura, or hard part (the 
facial) ; and portio mollis, or soft part (the auditory) of the 
" seventh " pair. 

The ninth pair in order, the glossopharyngeal, arc iiiixed 
nerves ; each being, partly, a nerve of taste, and, partly, a 
motor nerve for the pharyngeal muscles. 
11* 



250 



ELEMENTARY PHYSIOLOGY. 



The tenth pair is formed by the two pneumogastric nerves. 
These very important nerves, and the next pair, are the only 
cerebral nerves which are distributed to regions of the body 
remote from the head. The pneumogastric supplies the larynx, 
the lungs, the liver, and the stomach. 




Fig. 93. 

A diagram illustrating the arrangement of the parts of the brain and the origin of the 
nerves. — H, the cerebral hemispheres; C.S. corpus striatum; Th. optic thala- 
mus; P. pineal gland; Ft. pituitary body; C.Q. corpora quadrigemina ; Cb. 
cerebellum; J/, medulla oblongata ; I.-XII. the pairs of cerebral nerves ; Sp. 1, 
Sy. 2, the first and second pairs of spinal nerves. 



The eleventh pair again, called spinal accessory^ differ widely 
from all the rest, in arising from the sides of the spinal marrow, 
between the anterior and posterior roots of the dorsal nerves. 
They run up, gathering fibres as they go, to the medulla ob- 
longata, and then leave the skull by the same aperture as the 
pneumogastric and glossopharyngeal. They are purely motor 
nerves, while the pneumogastric is mainly sensory, or at least 
afferent. As, on each side, the glossopharyngeal, pneumogas- 
tric, and spinal accessory nerves leave the skull together, they 
are frequently reckoned as one pair, which is then counted as 
the eighth. 

The last two nerves, by this method of counting, become 



THE CEREBRAL NERVES. 251 

the ninth pair, but they are, really, the twelfilu They are the 
motor nerves which supply the muscles of the tongue. 

331. Olfactory and Optic Nerves. — Of these nerves, the 
two foremost pair do not properly deserve that name, but are 
really processes of the brain. The olfactory pair are prolonga- 
tions of the cerebral hemispheres ; the optic pair, of the walls 
of the third ventricle; and it is worthy of remark, that it is 
only these two pair of what may be called false nerves w^hich 
arise from any part of the brain but the medulla oblongata — 
all the other, trite nerves^ being indirectly, or directly, traceable 
to that part of the brain, while the olfactory and optic nerves 
are not so traceable. 

332. Effects of Injuries to the Medulla Oblongata. — 
As might be expected from this circumstance alone, the me- 
dulla oblongata is an extremely important part of the cerebro- 
spinal axis, injury to it giving rise to immediate evil conse- 
quences of the most serious kind. 

Simple puncture of one side of the floor of the fourth ven- 
tricle at once produces an increase of the quantity of sugar in 
the blood, beyond that which can be destroyed in the organ- 
ism. The sugar passes off by the kidneys, and thus this slight 
injury to the medulla gives rise to the disease called diabetes. 

More extensive injury arrests the respirator}^ processes, the 
medulla oblongata being the nervous centre which gives rise to 
the contractions of the respiratory muscles, and keeps the respi- 
ratory pump at Avork. 

If the injuries to the medulla oblongata be of such a kind 
as to irritate the roots of the pneumogastric nerve violently, 
death supervenes by the stoppage of the heart's action in the 
manner already described (p. 62). 

333. Crossing of Impulses in the Medulla. — The chan- 
nels of the afferent impulses, which are transmitted by the cord 
to the brain and awake sensation there, as we have seen, cross 
from one half of the cord to the other, immediately after they 
enter it by the posterior roots of the spinal nerves ; while the 
channels for the efferent, or volitional, impulses from the brain 



252 ELEMENTAEY PHYSIOLOGY. 

remain, throughout the cord, in that half of it from which they 
will eventually pass by the anterior roots. But, at the lower 
and front part of the medulla oblongata, these also cross cover ; 
and the white fibres which convey them are seen passing ob- 
liquely from left to right and from right to left in what is called 
the decussation of the miterior pyramids (Fig. 91). Hence, 
any injury, at a point higher up than the decussation, to the 
nerve fibres which convey motor impulses from the brain, 
paralyzes the muscles of the body and limbs of the opposite 
side. 

Division of one of the crura cerebri^ say the right, there- 
fore, gives rise to paralysis of the left side of the body and 
limbs, and the animal operated upon falls over to the left side, 
because the limbs of that side are no longer able to support its 
weight. 

But as the motor nerves given off from the brain itself do 
not cross over in this way, it follows that disease or injury at 
a given point on one side of the medulla oblongata, involving 
at once the course of the volitional motor channels to the spinal 
marrow and the origins of the cerebral motor nerves, will 
affect the same side of the head as that of the injury, but the 
opposite side of the body. 

If the origin of the left facial nerve, for example, be injured, 
and the volitional motor fibres going to the cord destroyed, in 
the upper part of the medulla oblongata, the muscles of the 
face of the left side will be paralyzed, and the features will be 
drawn over to the opposite side, the muscles of the right side 
having nothing to counteract their action. But it is the right 
arm, and the right leg and side of the body, which will be 
powerless. 

Section IV. — Unconscious Cerebration, 

334. Seat of Intelligence and Will— The functions of 
most of the parts of the brain which lie in front of the medulla 
oblonsfata are, at present, very ill understood ; but it is certain 



UNCONSCIOrS CEREBEATIOlSr. 253 

that extensive injury, or removal, of the cerebral hemispheres 
puts an end to intelligence and voluntary movement, and leaves 
the animal in the condition of a machine, working by the reflex 
action of the remainder of the cerebro-spinal axis. 

Thus there can be no doubt that the cerebral hemispheres 
are the seat of powers, essential to the production of those 
phenomena which we term intelligence and will ; but there is 
no satisfactory proof, at present, that the manifestation of any 
particular kind of mental faculty is especially allotted to, or 
connected with, the activity of any particular region of the 
cerebral hemispheres. 

335. Reflex Action of the Brain. — Even while the cerebral 
hemispheres are entire, and in full possession of their powers, the 
brain gives rise to actions which are as completely reflex as 
those of the spinal cord. 

When the eyelids wink at a flash of light, or a threatened 
blow, a reflex action takes place, in which the afierent nerves 
are the optic, the efferent, the facia!. When a bad smell causes 
a grimace, there is a reflex action through the same motor 
nerve, while the olfactory nerves constitute the afferent chan- 
nels. In these cases, therefore, reflex action must be effected 
through the brain, all the nerves involved being cerebral. 

When the whole body starts at a loud noise, the afferent 
auditory nerve gives rise to an impulse which passes to the 
medulla oblongata, and thence aff*ects the great majority of the 
motor nerves of the body. 

336. Reflex Actions in Reading Aloud. — It may be said 
that these are mere mechanical actions, and have nothing to do 
with the acts which we associate with intelligence. But let us 
consider what takes place in such an act as reading aloud. In 
this case, the whole attention of the mind is, or ought to be, 
bent upon the subject-matter of the book ; while a multitude 
of most delicate muscular actions are going on, of which the 
reader is not in the slightest degree aware. Thus the book is 
held in the hand, at the right distance from the eyes ; the eyes 
are moved, from side to side, over the lines, and up and down 



254 ELEMENTARY PHYSIOLOGY. 

the pages. Further, the most delicately adjusted and rapid 
movements of the muscles of the lips, tongue, and throat, of 
the laryngeal and respiratory muscles, are involved in the 
production of speech. Perhaps the reader is standing up and 
accompanying the lecture with appropriate gestures. And 
yet every one of these muscular acts may be performed with 
utter unconsciousness, on his part, of any thing but the sense 
of the words in the book. In other words, they are reflex acts. 

337. Artificial Reflex Actions — Education, — The reflex 
actions proper to the spinal cord itself are natural^ and are 
involved in the structure of the cord and the properties of 
its constituents. By the help of the brain we may acquire an 
infinity of artificial reflex actions. That is to say, an action 
may require all our attention and all our volition for its first, 
or second, or third performance, but by frequent repetition it 
becomes, in a manner, part of our organization, and is per- 
formed without volition, or even consciousness. 

As every one knows, it takes a soldier a long time to learn 
his drill — to put himself, for instance, into the attitude of " at- 
tention " at the instant the word of command is heard. But, 
after a time, the sound of the word gives rise to the act, 
whether the soldier be thinking of it or not. There is a story, 
which is credible enough, though it may not be true, of a prac- 
tical joker, who, seeing a discharged veteran carrying home 
his dinner, suddenly called out " xlttention ! " whereupon the 
man instantly brought his hands down, and lost his mutton 
and potatoes in the gutter. The drill had been thorough, 
and its effects had become embodied in the man's nervous 
structure. 

The possibility of all education (of which military drill is 
only one particular form) is based upon the existence of this 
power which the nervous system possesses, of organizing con- 
scious actions into more or less unconscious, or reflex, opera- 
tions. It may be laid down as a rule, that, if any two mental 
states be called up together, or in succession, with due fre- 
quency and vividness, the subsequent production of the one of 



UNCONSCIOUS CEREBRATION. 255 

them will suffice to call up the other, and that whether we de- 
sire it or not. 

The object of intellectual education is to create such indis- 
soluble associations of our ideas of things, in the order and 
relation in which they occur in nature ; that of moral educa- 
tion is to unite, as fixedly, the ideas of evil deeds with those 
of pain and degradation, and of good actions with those of 
pleasure and nobleness. 

338. The Sympathetic System. — Tha sympathetic system 
consists, chiefly, of a double chain of ganglia, lying at the 
sides and in front of the spinal column, and connected with 
one another, and with the spinal nerves, by commissural 
cords. From these ganglia nerves are given off, which for 
the most part follow the distribution of the vessels, but 
which, in the thorax and abdomen, form great net-works, 
or plexuses, upon the heart and about the stomach. It is 
probable that a great proportion of the fibres of the sympa- 
thetic system is derived from the spinal cord ; but others also, 
in all probability, originate in the gangha of the sympathetic 
itself. The sympathetic nerves influence the muscles of the 
vessels generally, and those of the heart, of the intestines, and 
of some other viscera; and it is probable that their ganglia 
are centres of reflex action to afferent nerves from these oro-ans. 

c 

But many of the motor nerves of the vessels are, as we have 
seen, under the influence of particular parts of the spinal cord, 
though they pass through sympathetic ganglia. 



CHAPTER XIII. 

HISTOLOGY; OPw, THE MINUTE STEUCTURE OF THE TISSUES. 

Section I. — Dermal Tissues. 

339. The Microscopical Analysis of the Body.— The va- 
rious organs and parts of the bod}'-, the working of which has 
now been described, are not merel}^ separable by the eye and 



256 



ELEMENTARY PHYSIOLOGY. 



tlie knife of the anatomist into membranes, nerves, muscles, 
bones, cartilages, and so forth ; but each of them is susceptible 
of a finer analysis, by the help of the microscope, into certain 
minute constituents which, for the present, are the ultimate 
structural elements of the body. 

340. Nuclei and Cells.— There is a time when the human 
body, or rather its rudiment, is of one structure throughout, 
consisting of a more or less transparent matrix, through which 
are scattered minute rounded particles of a difl'erent optical 
aspect. These particles are called nuclei ; and, as the matrix, 
or matter in which these nuclei are imbedded, readily breaks 
up into spheroidal masses, one for each nucleus, and these in- 
vesting masses easily take on the form of vesicles or cells, this 
primitive structure is called cellular, and each cell is said to be 
nucleated. 

As development goes on, the nuclei of this indifferent tissue 
simply increase in number, by division and subdivision ; but 
the substance in which they are imbedded, commonly called 




Pig. 94— Vertical section of a layer of epidermis, or epithelium, from its free to its 

decD surface. 
Fig. 95.— Lateral views of the cells Of which this layer is composed at the different 

heights, abed. 
Fig. 96.— Scales such as d viewed from their flat sides. 



DERMAL TISSUES. 



257 



the cell wall, and intercellular substance^ becomes very variously 
modified, both chemically and structurally, and gives rise to 
the peculiarities of the different, completely formed tissues. 

341. Epidermis and Epithelium. — Among these, the 
epidermis and some forms of epithelium present the simplest 
structure, next to the blood and lymph corpuscles described 
above (Chapter IV). These tissues are constantly growing in 
their deepest parts, and are, as constantly, being shed at their 
surfaces. 

The deep part consists of a layer of such globular nucleated 
cells, as have been mentioned, the number of which is con- 
stantly increasing by the spontaneous division of the nuclei and 
cells. The increase in number thus effected causes a thrusting 
of the excess of cell population toward the surface ; on their 
way to which they become flattened, and their walls acquire a 
horny texture. Arrived at the surface, they are mere dead 
horny scales, and are thrown off. 

Epithelium of the kind just described is called squamous. 
It is found in the mouth, and its scales may always be obtained 
in abundance by scraping the inside of the lip. 




Fig. 97. 

Ciliated epithelium. — a, the submncous vascular tissue ; 7), the deep layer of voung 

epithelium ceils; c, the cylindrical full-grown cells, with (c7)\he' cilia. 

In other parts of the alimentary tract, as in the intestines, 
the full-grown epithelial cells are placed side by side with one 
another, and perpendicular to the surface of the membrane. 
Such epithelium is called cylindrical (Fig. 58). 



258 



ELEMENTARY PHYSIOLOGY. 



In many glands (Fig. 56) the epithelial cells remain globu- 
lar^ and enlarging, eventually burst and disappear, to be re- 
placed by others. 

Ciliated epithelium is usually of the cylindrical kind, and 
differs from other epithelium only in the circumstance that one, 
or more, incessantly vibrating filaments are developed from the 
free surface of each cell. 




Fig. 100. 

Fig. 08.— A longitudinal and vertical section of a nail : «, the fold at the base of the 

nail ; &, the nail ; c, the bed of the nail. 
Fig. 99 is a transverse section of the same— C7, small lateral folds of the integument; 

6, nail ; c, bed of the nail, with its ridges. 
Fig. 100 is a highly-magnified view of a part of the foregoing— c, the ridges ; <f, the 

deep layers of epidermis ; e, the horny scales, coalesced into nail substance. 

342. Ifails. — In certain regions of the integument, the epi- 
dermis becomes metamorphosed into nails and hairs. 

Underneath each nail the deep layer of the integument is 



DERMAL TISSUES. 259 

peculiarly modified to form the bed of the nail. It is very vas- 
cular, and raised up into numerous parallel ridges, like elongated 
papilla? (Figs. 99, 100). The surfaces of all these are covered 
with growing epidermic cells, which, as they flatten and he- 
come converted into horn, coalesce into a solid continuous 
plate, the nail. At the hinder part of the bed of the nail, the 
integument forms a deep fold, from the bottom of which, in like 
manner, new epidermic cells are added to the base of the nail, 
which is thas constrained to move forward. 

The nail, thus constantly receiving additions from below 
and from behind, slides forward over its bed, and projects be- 
yond the end of the finger, where it becomes worn or cut off. 

343. Hairs. — A Aa^>, like a nail, is composed of coalesced 
horny cells, but instead of being only partially sunk in a fold 
of the integument, it is at first wholly enclosed in a kind of bag, 
the liair-sac^ from the bottom of which a papilla, which answers 
to a single ridge of the nail, arises. The hair is developed by 
the conversion into horn, and coalescence into a shaft ^ of the 
superficial epidermic cells coating the papilla. These coalesced 
and cornified cells being continually replaced by new growths 
from below, which undergo the same metamorphosis, the shaft 
of the hair is thrust out until it attains the full length natural 
to it. Its base then ceases to grow, and the old papilla and 
sac die away, but not before a new sac and papilla have been 
formed by budding from the sides of the old one. These give 
rise to a new hair. The shaft of a hair of the head consists of 
a central pith, or medullary matter, of a loose and open tex- 
ture, and sometimes containing air; of a cortical substance 
surrounding this, made up of coalesced elongated horny cells ; 
and of an outer cuticle^ composed of flat horny plates, arranged 
transversely round the shaft, so as to overlap one another by 
their outer edges, like closely-packed tiles. The superficial 
epidermic cells of the hair-sac also coalesce by their edges, and 
become converted into sheaths, which embrace the root of the 
hair, and usually come away with it, when it is plucked out. 

Two sebaceous glands commonly open into the hair-sac 



260 



ELEMEISTTARY PHYSIOLOGY. 



near its opening, and supply the hair with a kind of natural 
pomatum ; and delicate unstriped muscular fibres are so con- 
nected with the hair-sac, as to cause it to pass from its ordi- 
nary oblique position iuto one perpendicular to the skin, when 
they contract (Fig. 46). 

e dp J- 




Fig. 101. 

Part, of the shaft of a hair enclosed within its sac and treated with caustic soda, which 
has caused the shaft to become distorted. — or, medulla ; &, cortical part; c, cuticle 
of the shaft ; d and e, Inner and outer root-sheaths ; /, wall of the hair-sac. 

They are caused to contract by the influence of cold and 
terror, which thus give rise to '^ horripilation " or " goose-skin," 
and the " standing of the hair on end." 



Section II. — Interior Tissues, 

344. The Crystalline Lens. — The crystalline lens is com- 
posed of fibres (p. 210), which are the modified cells of the 
epidermis of that inverted portion of the integument, from 
which the whole anterior chamber of the eye and the lens are 
primitively formed. 

345. Cartilage. — ^While epithelium and epidermis are found 
only on the free surfaces of the organs, gristle, or cartilage, is 
a deep-seated structure (see Chapter VIII). It is composed 
of a semi-transparent, resisting, elastic matter, which yields the 
substance called chondrine by boiling, and contains a great 
number of minute cavities, in which lie single nucleated cells, 
or groups of such cells (Fig. 102). These cells increase in 
number by division. Cartilage contains no vessels, or only 
such as extend into it from adjacent parts. 



INTERIOR TISSUES. 



261 



346. Connective Tissue. — Connective Tissue (also called 
fibrous^ or areolar^ or sometimes cellular tissue). 



h p d 




Fig. 102. 

A section of cartilage, showing the matrix (a), with the groups of cells (&) contain- 
ing nuclei (c) and fat globules {d). 

This tissue, the most extensively diflfused of all in the body, 
consists of bands or cords, or sheets of whitish substance, 
having a wavy, fibrous appearance, and capable of being split 




Fig. 103. 



Fig. 104 



Connective tissue.— Fig. 103, unchanged— a, connective tissue ; ?>, fat cells ; Fig. IC^l, 
acted upon by acetic acid, and showing {a) the swollen and transparent gelatine- 
yielding matter, and ip) the elastic fibres. 



262 



ELEMENTARY PHYSIOLOGY. 



up mechanically into innumerable fine filaments. This tissue 
swells up and yields gelatine when it is boiled in water. The 
addition of strong acetic acid also causes it to swell up and be- 
come transparent, entirely losing its fibrous aspect ; and, further, 
reveals the presence of two elements which acetic acid does not 
affect, viz., nuclei and elastic fibres of different degrees of fine- 
ness. If the acid be now neutralized by a weak alkali, the 
connective tissue assumes its former partial opacity and fibril- 
lated aspect. The nuclei are the descendants of those which 
existed in the indifferent tissue from which the connective tissue 
has proceeded — while the elastic fibres, like the gelatine-yield- 
ing fibres, proceed from the metamorphosis of the matrix. 
The proportion of elastic fibre to the gelatine-yielding con- 
stituents of connective tissues varies, in different parts of the 
body. Sometimes it is so great that elasticity is the most 
marked character of the resulting tissue. 

Ligaments and tendons are simply cords, or bands, of very 
dense connective tissue. In some parts of the body the con- 
nective tissue is more or less mixed with, or passes into, carti- 
lage, and such tissues are called fihro-cartilages (see Chapter 
VIII.). 




Fig. 105. 



Fig. lOG. 



Fig. 107. 



Fat cells.— Fig. 105, having their natural aspect; Fig. 106, collapsed, the fat being 
exhausted ; Fig. 107, with fatty crystals. 

347. Fat Cells are scattered through the connective tissue, 
in which they sometimes accumulate in great quantities. They 
are spheroidal sacs, composed of a delicate membrane, on one 



INTERIOR TISSUES. 263 

side of which is a nucleus, and distended by fatty matter, from 
which the more solid fats sometimes crystallize out. Ether 
will dissolve out the fat, and leave the sacs empty and col- 
lapsed (Fig. 106). 

CoDsiderable aggregations of fat cells are constantly pres- 
ent in some parts of the body, as in the orbit, and about the 
kidneys and heart, but elsewhere their presence, in any quan- 
tity, depends very much on the state of nutrition. Indeed, 
they may be regarded simply as a reserve, formed from the 
nutriment which has been taken into the body in excess of its 
average consumption. 

348. Pigment-Cells are either epidermic or epithelial cells, 
in which colored granules are deposited, or they are particular 
cellular elements of the deeper parts of the body, in which a 
like deposit occurs. Thus the color of the choroid and of the 
iris arises from the presence of a layer of such cells. 

Section III. — Osseous Tissues. 

349. Structure of Bone. — ^Bone is essentially composed of 
an animal basis impregnated with salts of carbonate and phos- 
phate of lime, through the substance of which are scattered 
minute cavities — the laciince, which send out multitudinous 
ramifications, called canaliciili. The canaliculi of difterent 
lacuna) unite together, and thus establish a communication be- 
tween the different lacunae. If the earthy matter be extracted 
by dilute acids, a nucleus is constantly found in each lacunce ; 
and, not imfrequently, the intermediate substance appears mi- 
nutely fibrillated. In a dry bone the lacunae are usually filled 
with air. When a thin section of such a bone is, as usual, 
covered with water and a thin glass, and placed under the 
microscope, the air in the lacuna? refracts the light which passes 
through them, in such a manner, as to prevent its reaching the 
eye, and they appear black. Hence the lacuna^ were, at one 
time, supposed to be solid bodies, containing the lime salts oi 
the bone, and were called hone corpuscles (Fig. 110). 



26i ELEMEJ^TARY PHYSIOLOGY. 

All bones, except the smallest, are traversed by small 
canals, converted by side branches into a net-work, and con- 
taining vessels supported by more or less connective tissue and 
fatty matter. Those are called Haversian canals (Figs. 108, 
109). They always open, in the long run, upon the surface 
of the bone, and there the vessels which they contain become 
connected with those of a sheet of tough connective tissue, 
which invests the bone, and is called periosteum. 

In many long bones, such as the thigh-bone, the centre of 
the bone is hollowed out into a considerable cavity, containing 
great quantities of fat, supported by a delicate connective tis- 
sue, rich in blood-vessels, and called the marrow, or medulla. 
The inner ends of the Haversian canals communicate with this 
cavity, and their vessels are continuous with those of the mar- 
row. 

When a section of a bone containing Haversian canals is 
made, it is found that the lacunae are dispersed in concentric 
zones around each Haversian canal, so that the substance of 
the bone appears laminated; and, where a medullary cavity 
exists, more or fewer of these concentric lamellae of osseous 
substance surround it. 

350. How Bones grow. — This structure arises from the 
mode of growth of bones. In the place of every bone there 
exists, at first, either cartilage, or connective tissue hardly 
altered from its primitive condition of indiflferent tissue. When 
ossification commences, the vessels from the adjacent parts 
extend into the ossifying tissue, and the calcareous salts are 
thrown down around them. These calcareous salts invade all 
the ossifying tissue, except the immediate neighborhood of its 
nuclei, around each of which a space, the lacuna, is left. The 
lacunae and canaliculi are thus, substantially, gaps left in the 
ossific matter around each nucleus, whence it is that nuclei are 
found in the lacunae of fully-formed bone. 

Bone, once formed, does not remain during life, but is con- 
stantly disappearing and being replaced in all its parts. Never- 
theless, the growth of a bone, as a general rule, takes place 



OSSEOUS TISSUES. 



265 



only by addition to its free ends and surfaces. Tlins the bones 
of the skull grow in thickness, on their surfaces, and in breadth 




Fig. 108. 




Fig. 109. 




Fig. 110. 

Fig. lOS.— A transverse section of bone in the ncigbborliood of two Haversian canals, 

a a ; &, lacunie. 
Fig. 109. — A longitudinal section of bone with Haversian canals, d a, and lacuna, b 

(less magnified than the ]>receding). 
Fig. llO.—Lacima^ e, and canaliculi, c?, very highly magnified. 
12 



266 ELEMENTARY PHYSIOLOGY. 

at their edges, where they unite by sutures ; and when the 
sutures are once closed, they grow no more. 

The bones of the extremities, which are preceded by com- 
plete cartilaginous models, grow in two ways. The cartilage 
of which they consist grows and enlarges at its extremities un- 
til the bones have attained their full size, and remains to the 
end of life as articular cartilage. But in the middle, or shaft, 
of the bone, the cartilage does not grow with the increase in 
the dimensions of the bone, but becomes coated by successive 
layers of bone, produced by the ossification of that part of the 
periosteum which lies nearest, to the cartilage. The shaft of 
the bone thus formed is gradually hollowed out in its interior 
to form the medullary cavity, so that, at last, the primitive 
cartilage totally disappears. 

When ossification sets in, the salts of lime are not diffused 
uniformly through the whole mass of the preexisting cartilage, 
or connective tissue, but begin to be deposited at particular 
points called centres of ossification^ and spread from them 
through the bone. Thus, a long bone has usually, at fewest, 
three centres of ossification — one for the middle or shaft, and 
one for each end ; and it is only in adult life that the three 
bony masses thus formed unite into one bone. 

351. Structure of the Teeth. — Teeth partake more of 
the nature of bones than of any other organ, and are, in fact, 
partially composed of true bony matter, here called cement ; 
but their chief constituents are two other tissues, called dentine 
and enamel. 

Each tooth presents a crown, which is exposed to wear, 
and one or more tangs, which are buried in a socket furnished 
by the dense mucous membrane of the mouth, which consti- 
tutes the gum. The line of junction between the crown and 
the fang is the nech of the tooth. In the interior of the tooth 
is a cavity, which communicates with the exterior by canals, 
which traverse the fangs and open at their points. This cavity 
is the 'pul'p cavity. It is occupied by a highly-vascular and 
nervous tissue,, the dental pulp, which is continuous below, 



OSSEOUS TISSUES. 



267 



through the opening at the point of the fang, with the mucous 
membrane of the gum. 

The chief constituent of a tooth is dentine — a dense calci- 
fied substance containing less animal matter than bone, and 
further differing from it in possessing no lacunar, or proper 
canaliculi. Instead of these it presents innumerable, minute, 
parallel, wavy tubuli, which give off lateral branches. The 




Fig. 111. 

Fig. Ill, vertical— Fig. 112, horizontal section of a tooth. — a, enamel of the crown ; 
&, pulp cavity ; c, cement of the fangs ; c?, dentine. 



wider ends of these tubules open into the pulp cavity, while 
the narrower ultimate terminations ramify on the surface of 
the dentine, and may even extend into the enamel or cement 
(Fig. 115). 

The enamel consists of very small six-sided fibres, set 
closely, side by side, at right angles to the surface of the den- 
tine, and covering the crown of the tooth as far as the neck, 
toward which the enamel thins ofi* and joins the cement (Figs. 
113,114). 

Enamel is the hardest tissue of the body, and contains not 
more than two per cent, of animal matter. 

The cement coats the fangs, and has tlie structure of true 



268 



ELEMENTAEY PHYSIOLOGY. 



bone ; but as it exists only in a tliin layer, it is devoid of 
Haversian canals (Fig. 115). 

352. How Teeth are Developed.— The development of 
the teeth commences long before birth. A groove appears in 




Fia. 113. 





Fig. 114. 



Fig. 115. 



Fig. 113. — Enamel fibres viewed in transverse section. 

Fig. 114. — Enamel fibres separated and viewed laterally. 

Fig. 115.— A section of a tooth at the junction of the dentine (a) with the cement (e); 
&e, irregular cavities in which the tubules of the dentine end; c?, fine tubules 
contintted from them;/r/, lacunae and canaliculi of the cement. (All these 
figures are very highly magnified.) 



the gum of each side of each jaw ; and, at the bottom of this 
groove of the gum, five vascular and nervous papillae arise, 



OSSEOUS TISSUES. 269 

making twenty in all. The walls of tlie groove grow together, 
between and over each of the papillae, and thus these become 
enclosed in what are called the dental sacs. 

Each papilla gradually assumes the form of the future tooth. 
Next a deposit of calcific matter takes place at the summit of 
the papilla, and extends thence, downward, toward its base. 
In the crown the deposit takes on the form of enamel and den- 
tine ; in the root, of dentine and cement. As it increases it 
encroaches upon the substance of the papilla, which remains 
as the tooth pulp. The fully-formed teeth press upon the up- 
per walls of the sacs in which they are enclosed, and causing a 
more or less complete absorption of these walls, force their way 
through. The teeth are then, as it is called, cut 

The cutting of this first set of teeth, called deciduous, or 
milk teeth, commences at about six months, and ends with the 
second year. They are altogether twenty in number — eight 
being cutting teeth, or incisors ; four, eye teeth, or canines ; 
and eight, grinders, or molars. 

Each dental sac of the milk teeth, as it is formed, gives off 
a little prolongation of itself, which becomes lodged in the jaw, 
enlarges, and develops a papilla from which a new tooth is 
formed. As the latter increases in size it presses upon the 
root of the milk tooth which preceded it, and thereby causes 
the absorption of the root and the final falling out, or shedding, 
of the milk tooth, whose place it takes. Thus every milk 
tooth is replaced by a tooth of what is termed the permanent 
dentition. The permanent incisors and canines are lar^^er than 
the milk teeth of the same name, but otherwise difier little 
from them. The permanent molars, which replace the milk 
molars, are small, and have only two points in their crowns, 
whence they are called bicuspid. They never have more than 
two fangs. 

353. The Permanent Molars. — We have thus accounted 
for twenty of the teeth of the adult. But there are thirty-two 
teeth in the complete adult dentition — twelve grinders being 
added to the twenty teeth which correspond with, and replace, 



270 ELEMENTAEY PHYSIOLOGY. 

tliose of the milk set. When the fifth, or hindermost, dental 
sac of the milk teeth is formed, the part of the groove which 
lies behind it also becomes covered over, extends into the back 
part of the jaw, and becomes divided into three dental sacs. 
In these, papillae are formed and give rise to the great perma- 
nent back grinders, or molars^ which have fonr, or five, points 
upon their square crowns, and, in the upper jaw, commonly 
possess three fangs. 

The first of these teeth, the anterior molar of each side, is 
the earliest cut of all the permanent set, and appears at six 
years of age. The last, or hindermost, molar is the last of all 
to be cut, usually not appearing till twenty-one or twenty-two 
years of age. Hence it goes by the name of the " wisdom 
tooth." 

Section IV. — Muscular and Nervous Tissues. 

354. Muscle, Striated and Smooth. — Muscle is of two 
kinds, striated and smooth. Striated muscle^ of which all 
the ordinary muscles of the trunk and limbs consist, is com- 
posed of bundles of fibres, usually united at their ends to cords 
or sheets of connective tissue — the tendons (see Chapter VIIL). 
The bundles are enveloped in, and bound together by, connec- 
tive tissue, which supports the vessels and nerves of the mus- 
cle, and sometimes forms a dense sheath on its exterior, called 
^> fascia. 

Into the ultimate striated muscular fibre neither vessels, 
nor connective tissue, enter. Each fibre is, in fact, enveloped 
in a sheath formed by a tough, elastic, transparent, structure- 
less membrane, the sarcolemma (Fig. 119). 

The sarcolemma is not contractile, but its elasticity allows 
it to adjust itself, pretty accurately, to the changes of form of 
the contractile substance which it contains. 

This contractile substance, when uninjured, presents a very 
strongly-marked transverse striation, its substance appearing to 
be composed of disks of a partially opaque substance, in regu- 



MUSCULAE AND NERVOUS TISSUES. 



271 



lar alternation with others of a more transparent matter. A 
more faint longitudinal striation is also observable. "When 
the sarcolemma is torn, the contractile substance either divides 
into disks (Fig. 118), or more frequently and readily breaks 
up into minute Jihrillce (Figs. 116, 117), each of which, viewed 

Fig. 116. 




Fig. 118. 




Fig. 119. 
Fig. 116.— A miiscuiar fibre, devoid of sai-colcmnia, and breaking np at one end into its 

Fig. 117.— Separate fibrillar. 

Fig. 118.— A muscular fibre breaking up into disks. 

Fig. 119.— A muscular fibre, the contractile substance of which {a) is torn, while the 
sarcolemma (b) has not given way. 



by transmitted light, presents dark and light parts, which al- 
ternate at intervals exactly corresponding with the distance of 
the transverse striae in the entire fibre. Nuclei are obscrN cd 
here and there in the contractile substance within the sarco- 
lemma. 

In the heart, the muscular fibres are striated, and have the 



272 



ELEMENTARY PHYSIOLOGY. 



same essential structure as that just described, but tbey possess 
no sarcolerama. 

Smooth muscle consists of elongated band-like fibres, de- 
void of striation, each of which bears a rod-like nucleus. These 
fibres do not break up into fibrillse, and have no sarcolerama 
(Fig. 11). 




Fig. 120. « fi!!^ 



Fig. 121, 



Fig. 12a 



Fig. 120.— A Derve fibre in its fresb and unaltered condition. 

Fig. 121.— A nerve fibre in which the greater part of the sheath and coagulated ccm- 

tents {a b) have been stripped oflf from the axis cylinder (c c). 
Fig. 122.— A nerve fibre, the upper part of which retains its sheath and coagulated 

contents, while the axis cylinder (a a) projects. 
Fig. 123.— A ganglionic corpuscle— a, its nucleus. 

355. BTervous Tissue.— Nervous tissue contains two ele- 
ments nerve fibres and ganglionic corpuscles. Ordinary nerve 
fibres, such as constitute the essential constituents of all but the 
olfactory nerves, are, during hfe, or when perfectly fresh, sub- 
cylindrical filaments of a clear, somewhat oily, look. But, 
shortly after death, a sort of coagulation sets up within the 



MUSCULAR AND NERVOUS TISSUES. 



273 



fibre, and it is then found to be composed of a very delicate 
structureless outer membrane (wbich is not to be confounded 
with the neurilemma), forming a tube, through the centre of 
which runs a solid filament, the axis cylinder. Between the 
axis cylinder and the tube is a fluid, from which a solid, strongly 
refracting matter has been thrown down and lines the tube. 

Such is the structure of the larger nerve fibres, which lie, 
side by side, in the trunks of the nerves, bound together by 
delicate connective tissue, and enclosed in a sheath of the 
same substance, called the neurilemma. In the trunks of the 
nerve the fibres remain perfectly distinct from one another, 
and rarely, if ever, divide. But when the nerves enter the 
central organs, and when they are distributed, the nerve fibres 
frequently divide into branches. In any case, they become 
gradually finer and finer ; until, at length, axis cylinder, sheath, 




Papillae of the skin of the finger.— (7, a larsre papilla containinff a tactile corpuscle (e) 
with its nerve {d)\ &, other papillae, without corpuscles, but containing loops of 
vessels, c. 



and contents are not separable, and the nerve becomes a ho- 
mogeneous filament, the ultimate termination of which, in the 
sensory organs and in the muscles, is not yet satisfactorily 
made out. 

12'^* 



274: ELEMENTAEY PHYSIOLOGY. 

356. Tactile Corpuscles, — At page 181 mention is made 
of peculiar bodies called tactile corpuscles, oval masses of spe- 
cially modified connective tissue in relation witli the ends of the 
nerves in the papillae of the skin. In Fig. 124 four such 
papillae, which have been rendered transparent and stripped 
of their epidermis, are seen, and the largest contains a tactile 
corpuscle (c). 

In the central organs, on the other hand, it is certain that, 
in many cases, the fine ends of the nerve fibres are continued 
into the processes of the ganglionic corpuscles. 

The olfactory nerves are pale flat fibres, without any dis- 
tinction into axis, cylinder, and contents, but with nuclei set 
at intervals along their length. 

357, Ganglionic Corpuscles, — 6^an^Z2onic corpuscles are 
chiefly found in the cerebro-spinal axis ; in the ganglia of the 
posterior nerve roots, and in those of the sympathetic; but 
they occur also elsewhere, notably in some of the sensory 
organs (see Chapter X.). 

They are spheroidal bodies, containing a central cavity, in 
which a nucleus lies (Fig. 123, a), and sending off one, two, 
or more prolongations, which may divide and subdivide ; and 
which, in some cases, unite with the prolongations of other 
ganghonic corpuscles, while, \n others, they are continued into 
nerve fibres. 



PAET IL 
ELEMENTARY HYGIENE. 



CHAPTER XIV. 

SCOPE AND AIMS OP HYGIENE. 

358. Twofold Value of Knowledge. — Knowledge may be 
considered as having a twofold value, intellectual and practi- 
cal. In an intellectual point of view, all real knowledge, no 
matter how great or how small the subject, how near or how 
remote, how useful or how useless, has a value which is due to 
intrinsic truth, to the pleasure of its pursuit, and the mental 
benefits which result from its acquisition. The pure love of 
truth, for its own sake, is a very powerful incentive to the well- 
cultivated intellect, and is the main impulse which has prompt- 
ed to scientific research and the extension of the boundaries of 
knowledge. But it sometimes becomes so absorbing a passion 
as to obscure that value of knowledge which lies in its tises. 
Science elucidates the laws of nature, and the human mind 
has a high satisfaction in this work, but the principles of 
science have an exalted value in their applications to art, or as 
furnishino; enlio-htened rules of action. 

359. Practical Knowledge. — Knowledge has thus a prac- 
tical value; but by this I do not mean merely its application 
to productive occupations, as the mechanic arts or agriculture, 
although it has a high value here. By practical knowledge is 



276 ELEMENTARY HYGIEKE. 

to be properly understood that wliicli is capable of sending 
for guidance in the various circumstances of life, or wliicli 
has a definite bearing on human welfare. Man is a being 
constituted for action; all knowledge which will enable him to 
act most efficiently, which will help him to economize his 
energies and gain the largest results with the smallest expen- 
diture of force, is practical knowledge. He is an organized 
being of high complexity ; his system is liable to derangement 
from many causes, which produce bodily and mental suliering 
and disease ; the knowledge which is neceF,sary to avoid these 
results is practical knowledge. He is a social being, and capa- 
ble of varied enjoyment : whatever understanding of his own 
nature, or the laws and constitution of society, will help him 
to the discharge of his social duties, or enable him to increase 
his happiness, is also of the nature of practical knowledge. 

360. Applied Physiology. — In the previous part of the 
present work the student has been occupied in getting an un- 
derstanding of the truths of physiological science, or the ac- 
tions of the living system in normal conditions. This knowl- 
edge has two great practical applications : the first to Hygiene ^ 
or the art of preserving health ; and the second to Medicine^ or 
the art of restoring it. "When the vital machine has once be- 
come seriously deranged in any of its movements, profound 
knowledge and great skill and experience may be required to 
set it right again, and this is the work of the physician, who 
has to devote his life to professional study. But happily it 
requires less knowledge to keep what we already have than to 
recover it when lost. How to take care of the health, or to 
avoid many causes of disease, may be learned by all. That 
general acquaintance with the mechanism and working of the 
living system, which all persons, even moderately educated, 
should possess, is not only valuable to guard it against in- 
jury, but also to improve its various powers and capabilities. 
If life and its opportunities be valuable, what knowledge can 
compare in importance with that which teaches how it is to be 
prolonged and its various capacities augmented ? 



SCOPE AND AIMS OF HYGIENE. 2Y7 

361. False Conceptions of Disease. — In early ages it was 
the cuGtom to explain all effects in nature by supposing per- 
sonalities like our own which produced them. The air, the 
earth, the forest, the streams, the sea, were peopled with ima- 
ginary beings, who were believed to be the agents by which 
all the operations of nature were carried on. The regular ac- 
tions of the living system were thought to be due to spirits 
which inhabited it, and its disorders to the agency of evil 
spirits. Though these superstitions long since passed away, 
the ideas which replaced them involved errors of a kindred 
nature. Diseases were no longer considered as personal 
agencies to be driven out by exorcism, but there still lingered 
the idea that they were things, independent existences or en- 
tities, which were in some mysterious way thrust into the sys- 
tem, and " expelled " from it by the action of medicines. 
Vague notions of this kind still widely prevail, and great num- 
bers regard diseases as things that come arbitrarily, or are 
" sent " by Divine Providence as judgments or punishments 
for sins. 

Views of this kind are luifavorable to hygienic efforts. 
We can easily understand that minds fully possessed by them 
will tend to a passive acquiescence in what is felt to be un- 
avoidable, and the propitiation of Divine favor by fasting, 
humiliations, and prayers, will take the place of intelligent, 
vigilant, and systematic measures for the prevention of disease. 
In past times, indeed, such notions have operated as powerful 
hinderances to hygienic precautions. When quarantine regu- 
lations were first instituted to prevent the spread of contagion 
by ships from port to port ; and when vaccination was proposed 
as a preventive of small-pox, religious ideas were aroused into 
antagonism, and these beneficent measures were denounced as 
impiously contravening the Divine designs which employed 
plagues as scourges to punish the transgressions of mankind. 
In this way false theories of the nature and causes of disease 
acted as an obstruction to hygienic improvement. 



278 ELEMENTARY HYGIENE. 

362. The true Idea of Health and Disease.— Modern 
physiology has brought us to a better understanding of the 
subject. As stated in the first chapter, and as illustrated 
throughout the work, physiology is the science of vital power. 
Power is the accompaniment of material change, and the man- 
ifestation of all animal functions we have seen to be dependent 
upon vital transformations. Not only is the living body in 
constant visible movement, but in all its minutest parts and tis- 
sues there is an incessant metamorphosis — a rapid escape and 
renewal of the constituent atoms, and it is in this that life essen- 
tially consists. That active and unimpeded metamorphosis and 
prompt elimination of waste products which gives rise to the 
hicrhest and most via'orous life, constitutes Health : w^hile the 
obstruction, depression, or perversion of these vital changes 
constitutes Disease. We thus escape from the mischievous 
error that maladies are foreign intrusions — substantive exist- 
ences which get mysterious lodgment in the living organism, 
and find that they are simply disturbed physiological actions. 
A disease may consist in the loss of power to remove or ex- 
crete normal but injurious products ; or perverted transforma- 
tions may give rise to wrong products, and these may create 
still further disturbance, but in all cases the essence of disease 
is to be regarded as morbid activity. 

Gout^ for example, is a malady in which bad habits pervert 
the nutritive changes and originate morbid products ; — its chief 
peculiarity being the deposition of urate of soda in and about the 
joints. In health there is scarcely a trace of this salt to be 
found in the blood, and even this small proportion is being con- 
stantly thrown off*. Certain conditions of living, however, such as 
the habitual use of wines or malt liquors, and high feeding upon 
animal substances, attended with but little exercise, are known 
greatly to increase its quantity and seriously to interfere with 
its excretion. It is then deposited as a foreign or morbid in- 
gredient in the joints. Careful avoidance of the causes which 
give rise to this condition of the blood secures complete free- 



SCOPE AND AIMS OF HYGIEKE. 279 

dom from attack, even in those who may have inherited a 
strong predisposition to the disease. 

363. Control over the Causes of Disease. — We have seen 
how directly and vitally the great fiinctions of the system are 
dependent upon various conditions, such as diet, air, water, 
clothing, exercise, by which the healthy changes of life are 
carried forward. Those agencies, in their right action, are 
causes of health ; but when altered in their influence, they be- 
come causes of disease. The vital supply of gases, liquids, and 
solids, which maintain the transformations of life, if deficient 
in quantity or deteriorated in quality, speedily produces bodily 
derangement ; while just in proportion to the importance of 
these normal actions is the evil of their effects w^hen perverted. 
By the power which intelligence confers over these conditions, 
man has a large control over the causes of disturbed health. 
Diseases may baffle the physician's penetration and defy his 
remedial skill ; but, what is of far more importance, hygienic 
knowledge enables us to avoid them. The efficiency of pre- 
vention is proverbial, and we have examples of the value of 
sanitary knowledge and precautions on the most impressive 
scale. 

864. Examples of the Application of Hygienic Principles. 
— Cholera may be taken as an illustration. In former times, 
when sanitary questions were but little understood, the ap- 
proach of this terrible disease struck terror into the hearts of 
the people, who were powerless, as the pestilence swept away 
multitudes of the population of the principal towms. Its 
coming was awaited with a horrible dread ; and when it ap- 
peared, all efforts were addressed to the relief of those attacked, 
and medicines, though almost uniformly powerless, were, never- 
theless, almost the sole resource of the physician. But the 
connection between the disease and certain conditions, as filth, 
bad air, overcrowding, and irregularities of living, so common 
in cities, began at length to be perceived, and steps taken to 
remove the causes. The adequacy of these measures has been 
fully vindicated, and, with the knowledge that its conditions 



280 ELEMENTARY HYGIENE. 

are controllable, the predisposing alarms have ceased, the rav- 
ages of the epidemic have been greatly circumscribed, and 
there is the amplest experience to show that thorough, yet 
simple, measures of purijflcation are sufficient for its complete 
prevention. 

Another example is furnished by Scurvy. This disease, 
which, until recently, has been the scourge of the sailor and 
soldier, and for centuries was regarded as wholly beyond the 
power of remedies, also turns out to be fully preventable. 
'' There is no more interesting fact in the history of medicine 
than that this condition, which has been looked upon at various 
times as plague, as a mysterious infliction of Divine justice, 
against which man could only strive in vain, or as a disease 
inseparable from long voyages, should have been proved by 
evidence of a most satisfactory character to arise from causes 
in the power of man to prevent, and to be curable by means 
which every habitable country affords." Instead of inquiring 
into the conditions of its origin, and seeking means of preven- 
tion, the medical profession was for hundreds of years en- 
gaged in ransacking nature, with the hope of findinor some- 
thing that might prove an effectual remedy. This was souo-ht 
in vain until attention was turned to its cause, which vras 
found to consist in a lack of vegetable food, and the sim- 
ple precaution of famishing it has been the signal for the 
almost total disappearance of the disease. Many other illus- 
trations might be given of the efficiency of hygienic resources 
to arrest and prevent the spread of dangerous maladies, but 
they are needless. 

365. Remedial Influence of Hygienic Agencies. — Another 
important consideration deserves to be stated in this place : it 
is that hygienic measures have a most important remedial 
value. If the causes of health, when modified or perverted, 
become causes of disease, to whatever extent restorative medi- 
cines may be desirable, it is certain that the first dictate of 
wisdom is to rectify these wrongly-acting causes. Medical 
treatment, thus, has its hygienic resources, and, with the en- 



SCOPE AND AIMS OF HYGIENE. 281 

largement of rational experience, these resources are coming 
into greater and greater prominence. All who have watched 
the progress of the healing art in recent times, -will note that 
among the most enhghtened practitioners there has been a 
steadily diminishing confidence in medication, and an increas- 
ing reliance upon the sanitary influence of nature. It is noto- 
rious that in proportion to people's ignorance of their own con- 
stitutions and the true causes of disease, is their credulous 
confidence in pills, potions, and quackish absurdities, and 
while this ignorance continues, there will of course be plenty 
of doctors who will pander to it. And not the least of the 
benefits which will follow the better difiusion of physiological 
and sanitary information will be the protection of the com- 
munity from the numberless impostures of charlatanism and 
a better discrimination of the qualifications of competent phy- 
sicians. 

366. Hygienic Knowledge inevitably beneficial. — It is 
often said to be unnecessary to increase and diff'use knowledge 
on the subject of preserving health, as people will not use 
that w^hich they already have. It is true that often they do 
not ; and this is part of a still larger truth, that only rarely 
does human action completely conform to the state of intelli- 
gence. That derangement of the organism which constitutes 
a form of insanity, in which the intellect sees what is right, 
while the diseased impulses drive irresistibly tow^ard the wTong, 
is but a morbid exaggeration of the common experience of 
mankind, who "see the right, but still the wrong pursue." 
But when due allowance is made for the force of habit which 
urges people on in the old courses, after they are reprobated by 
the judgment, there will be found -still a constant tendency to 
adjustment between thought and action. Character, which is 
that organic stamp or moulding of human nature by which its 
actions are determined, adapts itself but slowly to ideal states; 
still, such adaptation is constantly going forward, and it is in 
this that human progress essentially consists. In the matter 
of hygiene, much, as ^ve have seen, has already been done to 



282 ELEMENTARY HYGIENE. 

make action harmonize with thought, while the more vividly 
truths are mentally realized, the more powerful will be the ten- 
dency to bring practice into conformity with them. While, 
therefore, it is not to be expected that, by the introduction of 
the study of physiology and hygiene into schools, disease will 
at once disappear, and everybody live to be a hundred years 
old, it is nevertheless certain that the diffusion of this kind of 
knowledge is the only road to amelioration. As it has 
already led to great improvement, it cannot fail, in future, to 
lead to still more extensive improvement. 

In the following chapters I propose to call attention to the 
various agents and activities which have a bearing, more or less 
direct, upon bodily and mental health. 



CHAPTER XV. 

AIR AND HEALTH. 

Section I. — Impurities of the Air, 

367. Constitution of the Atmosphere. — The chief constit- 
uents of the atmosphere are a pair of elements, oxygen and nit- 
rogen, and a pair of compounds, carbonic acid and watery 
vapor. The student will remember that, in treating of respira- 
tion (Chap, v.), it was stated that oxygen forms 21 per cent, and 
nitrogen 79 per cent, very nearly, of the bulk of the air. Oxy- 
geii is the hfe-sustaining element, and requires to be kept 
up to this standard for healthy respiration. Nitrogen is the 
negative or diluting element of the air. The proportion of 
carbonic acid varies from three to six parts in 10,000, while 
the watery vapor varies also from -^-^ to -g^ of the atmos- 
pheric volume. Minute traces of other substances may also 
be obtained, but the foregoing constituents, in the propor- 



IMPURITIES OF THE AIR. '2H6 

tions named, form the external atmosphere, or what is com- 
monly known as pure air. 

But air is rendered impure or unfit for respiratory pur- 
poses both hy disturbance in the proportion of its normal con- 
stituents, and by many substances in the shape of gases, vapors, 
and soKd particles which are thrown into it from numberless 
sources. Those arising from the habitations and works of 
men are of the most importance, in a hygienic point of view, 
both because we are constantly exposed to their influence, and 
because they are most completely subject to control. 

368. Their Relation to the Senses.— Many of these impuri- 
ties can be detected neither by taste nor smell, and are inhaled 
without any knowledge of their presence. Others are recog- 
nized at first ; but as the nerves soon lose their deUcate sensi- 
bility of discrimination, the senses are unreliable monitors. 
Hence, injurious influences, that do not result in immediate and 
painful disease, are generally apt to be neglected. There is, 
besides, a false logic in the case, it being inferred that, because 
the senses lose their susceptibility to morbific influences, the 
system therefore becomes accustomed and adapted to them, 
when they cease to be detrimental. But no error could be more 
pernicious, as it leads to carelessness and indifterence with 
respect to those insidious agencies which slowly and silently 
sap the foundations of health. Common instinct is sufficient 
to guard against palpable causes of injury ; intelligence alone 
can protect us from the latent and deeper agencies of physio- 
logical mischief. 

369. Carbonic Acid as an Impurity. — Tliis substance is 
constantly generated in the body, and is therefore, to a cer- 
tain extent, one of its natural constituents. But, when not 
promptly thrown from the system, its action becomes quickly 
injurious. The proportion of carbonic acid naturally existing 
in the atmosphere we may assume to be inoflensive, but all 
increase is deleterious. Air containing 1 per cent, of it is 
soporific, depressing, and produces dulness and headache. 
From 5 to 8 per cent, renders it dangerous to breathe, while 



284: ELEMENTARY HYGIENE. 

10 to 12 per cent, makes it speedily destructive to life. When 
breathed pure it causes suffocation. Air contaminated with 
it acts as a narcotic poison. The symptoms of poisoning by 
it are throbbing headache, with a feeling of fulness and tight- 
ness across the temples, giddiness, and palpitation of the heart. 
The pulse falls, respiration is slow and labored, the skin cold 
and livid, and convulsions and delirium ensue, which are fol- 
lowed by death. 

A cubic foot of air of average purity contains a little less 
than a cubic inch of carbonic acid. A cubic foot of air, as it 
comes from the lungs in ordinary respiration, contains up- 
ward of 70 cubic inches of carbonic acid. The quantity 
poured into the air by combustion is enormous. In Manches- 
ter, England, Angus Smith has calculated that 15,000 tons are 
daily thrown out. The products of firing pass into the exter- 
nal air, and, if gaseous, are rapidly difi'used, but those of light- 
ing are for the most part allowed to disseminate in the apart- 
ment. The combustion of 1 cubic foot of coal gas consumes 
the oxygen of 10 cubic feet of air, and produces 2 cubic feet 
of carbonic acid. The combustion of a pound of oil consumes 
the oxygen of 130 cubic feet of air, and produces about 21 
cubic feet of carbonic acid. A person, by breathing, adds 1 
per cent, of carbonic acid to 55^ cubic feet of air in an hour, 
which would vitiate to this extent 1 foot per minute, while 
this effect is much increased by the surface exhalations. These 
facts show the rapidity with which the breathing medium of 
inhabited apartments tends to become deteriorated. 

370. Watery Vapor as an Impurity. — Air saturated with 
moisture acts injuriously upon the system by refusing to re- 
ceive the perspiration which is offered to it by the skin and 
lungs. This produces the feeling of oppression and languor 
which even the most robust often feel in close and sultry days. 
By this obstruction of insensible perspiration, not only are the 
waste matters generated in the system unduly retained, but 
miasmas introduced through the lungs by respiration are pre- 
vented from escaping. This would lead us to expect a greater 



IMPURITIES OF THE AIR. 285 

prevalence of epidemic diseases in moist than in dry districts, 
a fact observed in the case of cholera, which follows the banks 
of rivers, and revels in damp, low situations. Moisture joined 
with warmth has a relaxing and weakening influence upon the 
body. The debilitating effect of the sirocco upon the system, 
and its lowering and dispiriting influence upon the mind, are 
due to a heated atmosphere surcharged with moisture. Air, 
cold and damp, has a pecuUarly chilling and penetrating efi"ect, 
as illustrated by the east winds of spring in New England. 

Dry air, by promoting the insensible perspiration, has a 
strengthening, exhilarating influence. Cold, dry air is invig- 
orating. Too dry an atmosphere, however, desiccates the 
exposed surfaces, and tends to inflame them. Dry climates, 
which quicken evaporation, are recommended for relaxed and 
languid constitutions, with profuse secretion, as in cases of 
humid asthma or chronic catarrh. 

371. Organic Matter. — This is a common impurity of the 
atmosphere, and is often present in dangerous proportions. 
It exists in the form of vapors, or suspended matters, and is 
found most abundantly diffused in the air of dwellings, hos- 
pitals, etc., and in the vicinity of decaying organic substances. 
In health it is thrown off" from the lungs by the process of 
respiration, and also by exhalation from the skin. The quan- 
tity has been estimated all the way from 10 to 240 grains per 
diem for each adult. It varies, however, with the circum- 
stances, the body excreting a much greater amount during a 
state of activity than when it is inactive. That coming from 
the lungs consists of an organic vapor, holding in suspension 
epithelium cells that have become detached from the mucous 
^urfiices of the air-passages, pharynx, mouth, etc. By the 
skin more is given out. Twice as much moisture loaves the 
body by this route as by the lungs, and it carries with it into 
the atmosphere fatty matters, epidermic debris, and also small 
quantities of urea. 

This organic matter, when drawn through sulphuric acid, 
darkens it ; through permanganate of potash, decolorizes it ; 



286 ELEMENTARY HYGIENE. 

and througli pure water, renders it offensive. It is probably 
in a state of combination with water, as the most hygroscopic 
substances, such as wool, feathers, and damp walls, absorb it in 
largest quantities. It has a peculiar, foetid smell, and on decom- 
position yields ammonia, being therefore nitrogenous. It is 
oxidized slowly, and is supposed to float through the air in 
clouds instead of undergoing rapid diffusion. The foetid odor 
of a bedroom in the morning, after it has been occupied 
during the night, well attests the presence of these organic 
vapors in the air. 

In the air of sick-rooms and hospitals organic matters ac- 
cumulate in large quantities unless there is the most thorough 
ventilation. In addition to the amount contributed by respi- 
ration, which is often much larger in sickness than in health, 
the exhalations from the skin are greatly increased, and large 
quvantities of effluvia also escape from the discharged evacu- 
ations. Moscatti, who condensed the watery vapor of a hos- 
pital ward at Milan, describes it as being " slimy, and having a 
marshy smell." The dust of a ward in St. Louis, in Paris, 
was discovered by Chalvert to contain, in one experiment, 36 
per cent., and in another, 46 per cent, of organic matter, which 
consisted chiefly of epithelium, and when burnt gave an odor 
of horn. Pus-cells have been discovered in the air of an oph- 
thalmic ward, and epithelium-cells are found in that of all ill- 
ventilated rooms. It is very likely that the specific poison of 
small-pox, scarlet fever, measles, diphtheria, etc., consists of 
molecular organic matter thrown off from the- skin and mucous 
surfaces. If not rapidly oxidized, it no doubt retains its poi- 
sonous properties, and through the medium of the atmosphere 
conveys the disease. It is also equally probable that the ema- 
nations from cholera evacuations may, through the medium of 
an impure atmosphere, propagate cholera. 

In the air of dwellings, starch-cells, particles of cotton, 
wool, etc., are very common. Injurious exhalations from the 
imperfect combustion of oil, tallow, gas, and other illuminating 
substances, are scarcely less so. 



IMPURITIES OF THE AIK. 287 

The action of these various forms of organic matter upon 
tlie system is regarded as directly poisonous. Hammond found 
in an atmosphere charged with this impurity, and from which 
the carbonic acid and moisture had been withdrawn, that a 
mouse died in 45 minutes. Dr. Parkes says that he has known 
cases "in which the inhalation of such an atmosphere for three 
or four hours produced in men decided febrile symptoms, in- 
creased temperature, quickened pulse, furred tongue, loss of 
appetite, and thirst, for even 24 or 48 hours subsequently." 

372. The Cellar a Reservoir of Bad Air. — Confined air, 
without access of sunlight, soon becomes dank and unwhole- 
some. In the cellars of dwellings this is a common condition 
during a large part of the year ; the confined air is loaded with 
decomposing organic matter, given off from the masses of de- 
caying vegetables with which they are stored. This foul air 
reaches the inhabitants of upper apartments in such small quan- 
tities as not usually to produce any marked manifestation of 
disease, yet dangerous fevers have often arisen from neglect 
of cleanliness in this particular. 

Section II. — Morbid Effects of Impure Air, 

373. In the Case of Various Trades. — The most palpable 
examples of the injurious effects of breathing contaminated 
air are furnished by the circumstances of certain industrial 
occupations. As a class, the miners of England break down 
prematurely from bronchitis and pneumonia, caused by the at- 
mosphere in which they live. The colliers of Durham and 
Northumberland, however, where the mines are well ventilated, 
do not appear to suffer from an excess of pulmonary disease. 
In the various trades, involving the inhalation of much dust 
by the workmen, bronchitis and its attendant disease, em- 
physema, are very common. In the pottery trade, this malady 
occurs so frequently as to be known as the *^ potter's asthma." 
Stone-cutters, grinders in steel, button-makers, workers in 
flax factories, etc., are all specially liable to bronchitis. Dr. 



288 ELEMENTARY HYGIENE. 

Grenhow states that, of 107 flax-factory operatives, whose 
cases were taken indiscriminately, 79 were suff"ering from bron- 
chial irritation, and in 19 of these there had been haemoptysis. 
Among 27 hacklers, 23 Averc diseased. The suspended parti- 
cles are drawn into the air-passages at each inhalation, and 
there find lodgment upon the delicate mucous surfaces with 
which they come in contact. The irritation thus set up dis- 
turbs the working of the lungs, and, if maintained, eventually 
ends in organic disease. 

Brass-founders, coppersmiths, plumbers, white-lead manu- 
facturers, house-painters, workers in mercury, match-makers, 
are all subject to pecuhar forms of disease produced by 
inhaling the fumes with which their business contaminates the 
air. These fumes gain access to the blood, and through this 
to the whole system, producing severe local disturbance in 
many cases, and always affecting the general health. 

374. Scrofula. — The accumulation of carbonic acid and 
organic matter in ill-ventilated dwellings, workshops, hospitals, 
and other places, by its depressing and disturbing inflnence 
upon the vital powers, is promotive of various disorders, but 
of none more generally than that imperfect and perverted 
state of the nutritive functions known as scrofula, Baudo- 
loque, an eminent French physician, affirms " that the repeated 
respiration of the same atmosphere is a primary and efficient 
cause of scrofula," and that " if there be entirely pure air, 
there may be bad food, bad clothing, and want of personal 
cleanliness, but that scrofulous diseases cannot exist." Again 
he says : " Invariably it will be found on examination that a 
truly sci'ofulous disease is caused by a vitiated air, and it is 
not always necessary that there should have been a prolonged 
stay in such an atmosphere. Often a few hours each day is 
sufficient, and it is thus that persons may live in the most 
healthy country, pass the greater part of the day in the open 
air, and yet become scrofulous, because of sleeping in a con- 
fined place where the air has not been renewed." 

When scrofula localizes itself in the lungs, there is pulmo- 



MORBID EFFECTS OF EVIPURE AIR. 289 

nary or tubercular consumption. The tubercles which in this 
disease make their appearance in the pulmonary organs, con- 
sist of crude, coagulated, half-organized masses of albumen, 
the abortive products of incomplete nutrition. In this manner, 
bad air, by producing the strumous condition, becomes a cause 
of consumption. It seems but natural to expect that the or- 
gans with which the foreign ingredients of the atmosphere 
come more immediately into contact, and the blood-vessels of 
which they must enter on their passage into the system, should 
feel in a distinctive manner their noxious influence. This ex- 
pectation is strengthened by observation and experiment upon 
both men and animals. It is a matter of common knowledge 
amongst physicians that where individuals habitually breathe 
impure air, and are exposed to the other debilitating causes 
which generally influence more or less the inhabitants of dark, 
ill-ventilated dwellings, scrofula, and consumption as one of 
its forms, are very apt to be engendered. In 1832, at Xor- 
wood School, in England, where there were 600 pupils, scro- 
fula broke out extensively among the children and carried off 
great numbers. This w^as ascribed to bad and insufficient 
food. Dr. Arnott was employed to investigate the matter, 
and immediately decided that the food "was most abundant 
and good," assigning "defective ventilation and consequent 
atmospheric impurity " as the true cause. 

375. Effects of the Air of Sick-Rooms. — The impurities 
of a sick-room atmosphere consist largely of organic matter, 
which not unfrequently bears the specific poison of the disease. 
This is the case with the exanthemata as well as with other 
contagious febrile aff'cctions. On uncovering a scarlet-fever 
patient in the direct rays of the sun, a cloud of fine dust may 
be seen to rise from the body — contagious dust, that in unven- 
tilated localities is but slowly dispersed or destroyed, and that 
may for days retain its poisonous qualities. Diseases of this 
character are undoubtedly propagated in other ways, but a 
confined atmosphere probably does more than all other causes 
put together toward aiding their diflusion, 
13 



290 ELEMENTARY HYGIENE. 

Besides bearing the specific poison, an atmosphere of this 
character is exceedingly depressing to those brought within 
the range of its influence. Interfering with the aeration and 
the nutritive capacity of the blood, it lowers the powers of the 
system, and thus paves the way for epidemic visitations of a 
malignant and fatal type. 

376. Effects of Iinpure Air upon the Course of Disease. 
— Foul air increases the severity of disease, rendering a fatal 
result much more probable, and, even if this is avoided, greatly 
prolongs the period of convalescence. It also predisposes to 
complications, and renders recovery more likely to be followed 
by subsequent trouble. This appears to hold true of all dis- 
eases, but especially of the febrile. It is known that in the 
treatment of typhus and typhoid fevers, the freest ventilation, 
even to the extent of placing the patient in the open air, re- 
duces their mortaUty more than half, and greatly shortens the 
time of recovery. A like provision in the treatment of scarlet 
fever, measles, small-pox, diphtheria, etc., not only renders them 
much less severe, but does away in a great degree with the 
necessity for medication, and also markedly diminishes the 
liability to those distressing sequelae which in less favorable 
conditions so often supen^ene. 

377. Consumpticn. — Probably those afflicted with con- 
sumption and other pulmonary complaints sulier more from 
the effects of foul air than any other invalids. The reason is 
obvious. The capacity of the lungs is more or less reduced, 
hence less air can be conveyed to the blood, and if this is de- 
ficient in oxygen and contains impurities, the blood is directly 
affected and the malady much aggravated. 

378. Its Efifects upon Inherited Taints. — Inherited ten- 
dencies to disease, particularly of a scrofulous character, are 
rapidly developed by impure air. The incompleteness of nu- 
trition gives strength to the lurking predisposition. Instances 
are constantly recurring in which consumptive tendencies are 
developed to a fatal issue through various bad conditions, 
impure air being the most potent agency. And physicians 



MORBID EFFECTS OF IMPURE AIR. 291 

are aware that the constant presence of a pure atmosphere, 
with other means for healthy nutrition, will hold the predis- 
position in check, and maintain the system above the plane 
of its influence. 

379. Morbid Mental Effects of Bad Air. — ^Breathing an 
impure atmosphere injures the mind as well as the body. If 
the blood which is sent from the lungs to the rest of the sys- 
tem is imperfectly aerated, no organ feels it more than the 
brain. Its immediate effect is to cloud the mind and depress 
its energy ; sharpness of attention, clearness of apprehension, 
and readiness of memory are all impaired. " The health of 
the mental and bodily functions, the spirit, temper, disposi- 
tion, the correctness of the judgment and brilliancy of the 
imagination depend directly upon pure air." 

Dr. Ray remarks : " In a school, or hospital, or other con- 
siderable assemblage of people, the purity of the air may be 
pretty accurately measured by the amount of cheerfulness, 
activity, and lively interest which pervades it ; and yet so 
little do people think or care about this subject, that under 
existing arrangements there are very few who do not every 
day of their lives inspire more or less highly vitiated air. The 
listlessness and stupidity of students, and especially of children 
confined in the school-room, are often due to the bad state of 
the air they breathe. Using the brain in a vitiated atmos- 
phere is like working with a blunted instrument, and the ctfoct 
of course must be aggravated where the inexperienced are first 
learning the use of the instrument. 



'"to 



Section III. — Purijication of the Air, 

380. Nature's Eesources. — The purification of the general 
atmosphere is maintained by various agencies. By the law 
of difiusion all gases intermingle, so that where impurities are 
set free at any point they tend to exhale, or ditliiso away, and 
thus become weakened and lost in the great body of the at- 
mosphere. Diffusion may take place through the chinks and 



292 ELEMENTARY HYGIENE. 

openings of rooras, but it proceeds so slowly tliat it is not to 
be relied upon for ventilation. The mixture of large masses 
of air and the dispersion and dilution of local impurities are 
also effected by the winds. Gaseous exhalations are washed 
out and absorbed from the atmosphere by the fall of rains. 
The earth's vegetation destroys carbonic acid, while the oxygen 
slowly burns up the numberless combustible vapors and con- 
taminations which are thrown into the air. By these means 
the earth's atmosphere is constantly maintained respirable and 
pure. 

381. Ventilation. — The object of ventilation is to extend 
these natural means of purification to the air of dwellings, hos- 
pitals, workshops, and, indeed, to all places where impurities 
are liable to accumulate and prove injurious. Taking the ex- 
ternal air as the standard of purity, it aims to conduct it 
through those places in a manner that, without inconvenience to 
their inmates, shall accomplish the rapid and thorough dilu- 
tion and transfer of whatever impurities their atmosphere may 
contain. To do this effectually and without risk to the health 
and comfort of the inmates, tho ventilation must conform to 
certain indispensable conditions. The air which enters must 
itself be pure. This may generally be secured by taking it 
from almost any exposed situation, unless there be some special 
source of impurity in close proximity. It is desirable, if pos- 
sible, particularly in cities, to introduce the air from a level a 
few feet above the surface, as there are more or less exhalations 
constantly floating in air next the ground. 

382. Amount of Air rec[uired. — It must be in sufficient 
quantity. We find Nature's standard of purity in the exter- 
nal atmosphere, and, other things equal, the nearer we ap- 
proach this in our dwellings, the healthier will be their in- 
mates. The earlier authorities on ventilation varied greatly 
in their estimates of the quantity necessary, some placing it as 
low as 60 cubic feet per head per hour, while others consid- 
ered 500 cubic feet as not too much. More thorough investi- 



PURIFICATION OF THE AIR. 293 

gallons have since been made, and it is found that even the 
highest of these estimates is quite insufficient. 

The object to be attained is so to dilute the products of 
respiration and transpiration, and of combustion and lighting, 
as to keep the air always pure and fresh. The successive ex- 
periments made by Grassi and others have shown that allow- 
ances successively given of 10 cubic metres (rrr 353 cubic feet), 
of 20 cubic metres (== 706 cubic feet), of 30 cubic metres { = 
1,059 cubic feet), were not enough for one man, and the quan- 
tity was gradually increased till 60 cubic metres (2,118 cubic 
feet) were allowed. The air in the cell of a prisoner who re- 
ceived this ration seemed pure to the senses. Dr. Parkes 
says : *' From a number of experiments in which the outflow 
of air was measured, and the carbonic acid simultaneously de- 
termined, I have found at least 2,000 cubic feet per hour must 
be given to keep the carbonic acid at 5 or 6 per 1,000 vol- 
umes, and to entirely remove the fa3tid smell of oro-anic mat- 
ter." Dr. Sankey, from careful experiments with a ventilating 
fan, found that, when in a ward in the London Fever Hospital 
800 cubic feet per head per hour were supplied, the ventilation 
was insufficient. 

It has been stated, from extensive observations, that in 
mines, if it be wished to keep up the greatest energy of the 
men, no less than 100 cubic feet per man per minute (= 6,000 
cubic feet per hour) must be given. If the quantity is reduced 
to one-third, or even one-half, there is a decided diminution in 
the amount of work performed. 

If possible, the supply for the sick should be unlimited. 
In some diseases, so much organic matter is thrown off, that 
scarcely any ventilation is sufficient to remove the odor. Such 
diseases as pyaemia, typhus and typhoid fevers, small-pox, and 
the like, are best treated in the open air. This is found of the 
utmost value, more important even than diet and medicines. 
Grassi mentions that the air in a ward in the Hospital Xockcr, 
in Paris, was perceptibly tainted by emanations from a can- 



294 ELEMENTARY HYGIEXE. 

cerous ulcer, although the ventilation at the time was 3,500 
cubic feet per head per hour. 

383. Heating the Air. — The temperature of the air must 
be carefully regulated. In this climate, cooling the air is rarely 
necessary, but in the colder months of the year the incoming 
air requires to be warmed sufficiently for comfort, and in such 
manner as not to disturb the normal proportions of its con- 
stituents. The great danger is that of overheating it, whereby 
its capacity for moisture is greatly increased and ventilation 
becomes converted into a kiln-drying process scarcely less in- 
jurious than impure air. The policy should be to introduce 
large quantities of air raised only to a proper breathing tem- 
perature (60° to 70*^ Fab.), the temperature to be maintained 
by a steady and rapid change, so directed as to remove the 
cooler air of the apartment, and replace it with that freshly 
warmed. It may be said that this involves a much greater 
loss of heat than the opposite course, viz., the raising to a 
high temperature of small quantities of air. Even if this were 
true, which is not the case, waste of heat would be far prefer- 
able to the loss of health, w^hich the latter process involves, 
both by the increased drying power it gives the air, and by 
insufficient ventilation. 

The heat imparted to the air in this process becomes a 
means of promoting its movement. With this as a motive 
power, by the aid of flues and ventilating shafts, very thorough 
purification may be obtained. 

384. Eate of Movement. — The motion of the air must be 
imperceptible. Air may move at the rate of 100 feet per 
minute without violating this requirement ; but it is a much 
greater velocity than is needed for ventilating purposes ; that 
is to say, after the air has once entered the apartment. In the 
flues, of course, a much greater velocity is necessary. If there 
is little or no interference from outside cuiTcnts, the air within 
the building may readily be made to move in a body from 
above downward, and the rapidity of its movement can be 
easily regulated. It may be objected to this downward move- 



PURIFICATION OF THE AIR. 295 

raent that the natural tendency of impurities is upward, with 
the course of the warmer air, and that by being made to take 
a downward direction they are brought back again to be re- 
inhaled. If it were true that the impurities, as such, imme- 
diately rose to the ceiling and escaped from the apartment, 
the objection would hold ; but this is not the case. On 
the contrary, it is known that the carbonic acid and other 
gaseous impurities are equally diffused, and the weight of the 
organic substances and other suspended matters leads to the 
inference that they would gravitate toward the floor, particu- 
larly when rising currents of warm air are excluded, as they 
should be, by introducing it at the top of the room. In no 
other way can so steady and equable a movement be obtained 
as by introducing the warm air at the top and removing it 
below ; and, apart from any theoretical considerations, it is 
found to yield excellent practical results. 

385. Other Means of Purification. — In certain special 
cases where the air is being rapidly contaminated by foul 
or poisonous exhalations, and where, either from confinement 
or other cause, the purifying agencies of nature are unable to 
work with sufficient rapidity and vigor, recourse is had to 
various chemical substances, with a view to the immediate de- 
struction of such emanations. The more common substances 
used as deodorizers and destroyers of foul emanations are char- 
coal, compounds of chlorine (or mixtures which evolve this 
gas), nitrous acid, and sulphurous acid. 

Charcoal presents an immense absorbent surface to the 
air, a cubic inch of beechwood coal equalling in surface 100 
square feet (Liebig). It is therefore a powerful oxidizer of 
organic matter, catching and holding the particles in contact 
with oxygen, already within it, until their destruction is accom- 
plished. Its eff'ects are especially marked with sewa<^e o-ascs 
and with the organic emanations in disease. Of the different 
kinds, animal charcoal is regarded as best for disinfecting pur- 
poses. 

Permanganate of Potas\ or Soda [Condys Fluid), gives 



296 ELEMENTARY HYGIENE. 

off oxygen, and rapidly destroys organic matter. Ammoni- 
acal compounds are at once decomposed. Permanganate of 
soda, taken into the mouth, quickly destroys the odor of to- 
bacco (Hoffman). 

Compounds of chlorine act through the liberation of 0110- 
rine gas, which rapidly decomposes sulphuretted hydrogen and 
sulphide of ammonium, and also destroys organic odors. It 
may be obtained by moistening chloride of lime, or soda, Tvhen 
it slowly escapes into the atmosphere. It is also easily evolved 
by mixing 1 paii: of powdered binoxide of manganese with 4 
parts of common salt and 4 of dilute sulphuric acid. A gentle 
heat will aid the evolution. The gas, however, will corrode all 
exposed metallic surfaces. 

Nitrous acid may be evolved by placing nitre in sulphuric 
acid, or by dropping a bit of copper into dilute nitric acid. It 
is a very efficient disinfecting agent, but irritating to the air- 
passages and lungs. The ease with which it yields up a por- 
tion of its oxygen makes it a powerful oxidizer, which acts 
rapidly upon organic emanations. Sulphurous acid is given 
off when sulphur is burned. It decomposes sulphuretted hy- 
drogen, and acts with energy upon organic substances. 



CHAPTER XVI. 

WATEE AND HEALTH. 

Section I. — Physiological Offices of Water. 

386. Amount in the Body.— The student is aware that 
water is a very large constituent of all parts of the body. The 
bones contain 130 parts of it in 1,000; muscle, ^50; brain, 
789 ; blood, 795 ; and it forms nearly three-foui-ths the entire 
weight of the body. 



PHYSIOLOGICAL OFFICES OF WATEE. 297 

387. It is the Instrument of Change.— Water gives ful- 
ness and flexibility to the softer tissues, and is the great agent 
of movement within the system. It performs the same office 
of transportation and exchange in the vital economy that it 
does by oceans, rivers, and canals in the commerce of the 
world. Nutritive substances cannot enter the system, nor the 
debris of the tissues leave it, except in a state of solution ; it is 
the office of water to bring them into this condition, and con- 
vey them to their various places of destination. 

388. Its Solvent Power. — Water performs these duties by 
virtue of its remarkable powers as a solvent. Perfectly neutral 
itself, it becomes sweet, spur, salt, astringent, hitter, or poison- 
ous, accordingly as the bodies it dissolves possess these proper- 
ties. It readily takes up either gaseous, liquid, or solid sub- 
stances, and thus becomes a means for their rapid and wide- 
spread diffusion. 

389. Quantity daily taken. — Water is taken not only in 
the form of drink, but it is a large constituent of the various 
food-stufls ; hence any estimate of the quantity passing into the 
system, to be reliable, must include both these sources of sup- 
ply. It has been found that a healthy adult man ordinarily 
takes from 70 to 90 ounces in 24 hours. The amount, how- 
ever, varies greatly in different circumstances, sometimes, from 
individual peculiarities, falling much below, and at other times 
considerably exceeding this figure. 

390. Its Excretion. — Water is constantly escaping from 
the system, cither in a fluid or vaporized form, and carries with 
it the various substances resulting from the wear and tear of 
the tissues. Of all that is expelled, about 48 per cent, is dis- 
charged with the urine and faeces, and about 52 per cent, by 
the lungs and skin. Of the latter, the skin discharges nearly 
twice as much as the lungs. 

Section IT. — Different Vinds of Water. 

391. Its Foreign Ingredients. — Owing to its extraordi- 
narily solvent power, water, in a natural condition, is never 

13-^* 



298 ELEMENTAKY HYGIENE. 

found free from foreign ingredients, which modify its char- 
acter according to the quantity present, and their own pecu- 
liar properties. This gives rise to the several varieties 
that we know as hard-water, soft-water, mineral-water, and 
sea- water. 

392, Soft-Water. — This is water that gives a feeling of 
softness in washing, from the absence of certain mineral sub- 
stances, which render it rough or hard. Rain-water may be 
taken as a fair example, for when caught in the open country, 
it is the purest water that Nature provides. It is not entirely 
free from foreign matters, however, for, as it falls through the 
air, it absorbs oxygen, nitrogen, carbonic acid, ammonia, and 
organic substances, and also washes out any impurities which 
the atmosphere may happen to contain. Thus, in the vicinity 
of the ocean the air contains traces of common salt ; in the 
neighborhood of cities, various saline, organic, and gaseous 
impurities, while dust is raised from the ground and scattered 
through it by winds. These are all rinsed out of the air by 
rain. In passing through it, water becomes highly aerated ; 
that is, acquires an atmosphere of its own, which contains from 
ten to fifteen per cent, more oxygen than ordinary air. This 
gives to water its agreeable taste. 

Soft water, which is free from dissolved mineral matters, 
makes its way into organized tissues with much more readiness 
than hard water. It also exerts a more powerful solvent, or 
extractive action, and is thus a better vehicle for conveying 
aUmentary substances into the living system. In culinary 
operations, where the object is to soften the texture of animal 
and vegetable compounds, or to extract from them and present 
in a liquid form some of their valuable parts, as in making 
soups, broths, stews, or infusions, as tea and coffee, soft water is 
much to be preferred. 

In consequence of its aeration, rain-water is both healthy 
and pleasant as a beverage. The greatest benefits have re- 
sulted in many cases from its use, where the spring and well 
waters were largely impregnated with earthy salts. 



DIFFERENT KINDS OF WATER. 299 

393. Hard Water. — Rain-water, as it penetrates the 
ground, absorbs a large proportion of carbonic acid from the 
air in the interstices of the soil, whicli is 250 times richer in 
this gas than the air above. The presence of this absorbed 
carbonic acid greatly increases the solvent power of water upon 
mineral substances. Passing more or less deeply into the 
earth, it dissolves various substances which it meets ; hence 
the difference between spring and well waters, which are gen- 
erally hard, and rain-water, which has not come in contact 
with the ground. The life and sparkle of spring and well 
water are due to the presence of carbonic acid thus taken up, 
and when this is found in a considerable degree, it is safe to 
infer the additional presence of large quantities of saline impu- 
rities. The usual ingredients of well and spring water are lime, 
magnesia, soda, and oxide of iron, combined with carbonic and 
sulphuric acids, which form carburets and sulphates. Common 
salt is also often present. The most usual ingredients, how- 
ever, are carbonate and sulphate of lime. Carbonate of lime, 
or limestone, is not soluble in pure water, but dissolves in 
water containing free carbonic acid. 

The amount of mineral matter found in water varies greatly. 
The water of the river Loka, in Sweden, which flows over in- 
soluble granite, contains only -^^ of a grain of mineral matter 
in an imperial gallon. Common well and spring waters con- 
tain from 5 to 70 grains per gallon. Sea-water contains 2, GOO 
grains to the gallon ; and that from some parts of the Dead 
Sea, or the Great Salt Lake of Utah, as much as 20,000 grains 
to the gallon. 

394. Mineral Waters are usually those of springs which 
are highly charged with one or more mineral ingredients. 
Those abounding in salts of iron are called chahjhcate waters. 
If the waters are brisk and sparkling, carbonic acid is present, 
and they are termed cai-honated, or acidulous. 

395. Limestone Waters. — These arc also clear, sparkling 
waters, of agreeable taste. They ditler from the Avater of chalk 
districts, in containing more sulphate of lime and los^ carbon- 



300 ELEMENTARY HYGIENE. 

ate, and in dolomitic districts much sulphate and carbonate of 
magnesia. They contain little organic matter, but are very 
hard, soften little on boiling, and are generally unwholesome. 

396. Sand and Gravel Waters.^These vary in character 
in different regions. Some are very pure, containing less than 
5 grains of mineral matter in a gallon^ and less than 1 grain of 
organic matter. Others again, particularly such as flow over 
soft sand-rock, are liable to be very impure, containing much 
chloride of sodium, carbonate of soda, iron, and a little lime 
and magnesia, amounting altogether to from 30 to 80 grains 
per gallon. The organic matter may also be in large amount, 
from 4 to 10 grains per gallon, or even more. 

397. Alluvial Waters, — These are generally highly 
charged with carbonate of lime, sulphate of lime, sulphate of 
magnesia, chloride of sodium, carbonate of soda, iron, silica, 
and often with organic matter. The amount of solids per 
gallon ranges from 20 to 120 grams. 

398. Surface and Sub-soil Water. — This is often very 
impure. Cultivated lands, with rich, manured soils, furnish a 
water often containino- both oro-anic matter and salts in larcfe 
quantity. In tov/ns, and among the habitations of men, the 
surface and shallow well-water frequently contains large quanti- 
ties of nitrites and nitrates, sulphates and phosphates of lime, 
and soda and chloride of sodium. Organic matter, also, exists 
often in large amount. 

399. Marsh-Water. — This is always impure from the 
presence of much organic matter, wdiich is chiefly of vegetable 
origin, and varies in quantity from 10 to 50 grains in the gal- 
lon. The proportion of mineral ingredients is usually small, 
unless the marsh be salt, when the mineral constituents of sea- 
water are present. 

400. River- Water. — This varies much in the number and 
quantity of its constituents. Coming from various sources, it 
is even more complex in constitution than spring or well water. 
Oftentimes it is greatly contaminated by the sewage of towns 
and the refuse of manufacturing operations which are carried 



DIFFERENT KINDS OF WATEE. 601 

on along its banks, and it is also likely to contain a large 
amount of organic matter. 

401. Sea-Water. — The solid constituents of sea-water 
amount to about 3|- per cent, of its weight, or nearly half an 
ounce to the pound. It is unfit for use unless distilled. It 
then answers well for cooking purposes, and, if thoroughly 
aerated, is palatable. Any organic matter remaining after dis- 
tillation may be removed, by passing the water through a 
charcoal filter, or by letting it stand for a few days. Care 
should be taken that no lead finds its way into distilled water, 
as it is rapidly taken up. Many cases of lead-poisoning have 
occurred on board ships, partly from the use of minium in the 
apparatus, and partly from the use of zinc pipes, with lead in 
their composition. 

402. Purity of Water. — Perfectly pure water can only 
be obtained by the most careful processes of distillation, and is 
never found as such in a natural state. Hence the difficulty 
of defining what are properly impurities, particularly when we 
bear in mind the fact that water containing considerable quan- 
tities of foreign matter may be used for long periods together, 
without producing any recognizably injurious results. Expe- 
rience has shown, however, that certain conditions are neces- 
sary to health, and cannot be neglected with impunity. The 
water should be transparent and colorless, free from odor, and 
without taste. It should also be well aerated, and aftbrd no 
deposit on standing; above all, it should be free from organic 
matter. Probably the less it contains of saline ingredients the 
better. The Sanitary Congress held at Brussels, in 1853, de- 
cided that the total amount ought not to exceed 85 grains per 
gallon. But this furnishes no reliable criterion, as a far loss 
quantity of sulphate of lime, or magnesia, is known to bo in- 
jurious, while the proportion of carbonate of lime, or soda, 
may considerably exceed this, and produce no manifestly bad 
eftects. 

403. Organic Impurities in Water. — Those vary exceed- 
ingly in character and amount, and may bo either nioohanioally 



302 ELEMENTARY HYGIENE. 

suspended or dissolved in the water. If suspended, and of 
vegetable origin, their presence will often be indicated by a 
peculiar yellowish or brownish tinge, such as most are familiar 
wdth in the water of marshes or peat-bogs. If of animal origin, 
they may impart no tinge, and are more likely to be dissolved. 
They are derived from numberless sources, but those of most 
importance, hygienically, are furnished by the habitations and 
trades of men. Rain-water carries down from the air floating 
organic impurities, and it may also become contaminated by 
decaying leaves that have accumulated on the roofs of houses. 
Cisterns are also liable to receive impurities from the leaking 
of sinks or waste-pipes, or by the washing in of leaves from the 
roof. Shallow wells are extremely apt to become contami- 
nated by floods. carrying in organic surface impurities. Deep 
wells frequently drain large areas about them, and are very 
often, particularly in towns, rendered impure and even offensive 
by collecting the drainage from cess-pools, vaults, etc. In epi- 
demics of typhus and typhoid fever and cholera, cases have 
occurred where it was known that th^ specific poison of the 
disease found its way into the system by this means. Springs 
and streams oftentimes receive the discharges from large man- 
ufactories ; and although the water appears pure, an exami- 
nation reveals the presence of organic matter. The effects of 
this contamination may be shown by taking a little of the 
sediment that has accumulated at the bottom of a cistern, and 
placing it in a bottle of perfectly pure distilled water, when in 
a short time, if the weather be warm, it will smell ofiensively. 
Thus, at ordinary summer temperatures, this organic matter is 
liable to undergo putrefactive change, and it is then that it ex- 
erts its most baneful effects upon the system. This is, no 
doubt, one of the causes of the greater prevalence of diarrhoeas 
aud dysenteries during the warmer portions of the year. 

Section III. — Morbid Effects of Impure Water. 
404. Dyspepsia. — Water containing sulphate of lime, chlo- 
ride of calcium, and the magnesia salts, has a decided tendency 



MORBID EFFECTS OF IMPURE WATER. 303 

to produce stomachic and intestinal derangements. Dr. Suth- 
erland found that the hard water of the sandstone rocks, which 
was formerly much used in Liverpool, exerted a marked effect 
in producing constipation, loosening the secretions, and causinsc 
visceral obstructions ; and in Glasgow, the substitution of soft 
for hard water, according to Dr. Leech, lessened the prevalence 
of dyspeptic complaints. The exact amount capable of pro- 
ducing these symptoms has not been determined. In a w^ell- 
water which was found so injurious that men would not drink 
it, there were present 19 grains of carbonate of lime, 11 grains 
of sulphate of hmc, and 13 grains of chloride of sodium per 
gallon. The total solids were 50 grains per gallon. Iron, in 
quantities sufficient to give the water a slightly ferruginous taste, 
often produces dyspepsia, headache, and general uneasiness. 

405. Diarrhoea. — That this disease often originates in the 
use of bad water, there is no doubt. Great numbers of in- 
stances are on record where it was traced directly to this 
cause, and where its removal was followed by a disappearance 
of the disease. 

Mineral matters, either dissolved or suspended, will give 
rise to it if present in considerable quantity. The water of 
many rivers holds in suspension fine particles of clay or marl 
in great abundance, particularly at certain seasons, and, 
if drank for any length of time, wall produce diarrhoea. 
Hammond instances the Mississippi, Missouri, Rio Grande, and 
Kansas Rivers as examples. The use of waters containing dis- 
solved mineral substances, particularly sulphates, will also cause 
diarrhoea. *' Parent Duchatelet noticed the constant excess 
of patients furnished by the prison of St. Lazare, in conse- 
quence of diarrhoea, and he traced this to the water, which 
* contained a very large proportion of sulphate of lime and 
other purgative salts ' " (Parkes). Waters impregnated with 
nitrate of lime will produce diarrhoea. Brackish ^Yater acts in 
the same way, probably from the large quantity of chloride of 
sodium it contains. 

Dissolved or suspended organic matter, whether of vegetable 



304: ELEMENTAEY HYGIEKE. 

or animal origin, will cause diarrhoea. In the recent war, 
great numbers of cases occurred from the use of marsh or 
ditch water, which ceased when wells were sunk. Water con- 
taining foDcal matter, sulphuretted hydrogen, or other sewage 
products, often occasions the worst forms of diarrhoea, attended 
sometimes with marked choleraic symptoms — such as purging, 
vomiting, and cramps — even when the senses give no indica- 
tion of these impurities. 

The effects of sulphuretted hydrogen are well shown by a 
case that occurred in the recent war in Mexico. The French 
troops suffered greatly at Orizaba, from the use of water taken 
from sulphurous and alkaline springs. This produced dyspep- 
sia and diarrhoea, attended with enormous eructations after 
meals, the eructed gas having a strong smell of sulphuretted 
hydrogen. Sewage gases, setting back through untrapped 
overflow pipes into tanks and cisterns, often contaminate the 
water very rapidly. 

408. Dysentery — This also frequently results from the use 
of impure water. The impurities which produce it appear to 
be of the same kind as those which cause the allied condition 
of diarrhoea. The drainage from grave-yards contains large 
quantities of organic matter and nitrates, and its use is very 
liable to produce this disease. Water contaminated by the 
discharges of dysenteric patients is known to produce dysen- 
tery in others, and thus the disease oftentimes becomes 
epidemic. 

407. Cholera. — Symptoms of this malady often follow 
the use of water containing sewage or decomposing organic 
matter. Many believe that it is capable of producing the dis- 
ease, but this point is still unsettled. The use of water ren- 
dered impure by the presence of choleraic evacuations, how- 
ever, is known to give rise to the disease in others, and in 
towns this is found a ready means of propagation. 

In addition to the production of cholera from drinking 
water containing cholera-stools, it is quite certain that the use 
of impure water of any kind predisposes to cholera, though it 



MORBID EFFECTS OF IMPURE WATER. 305 

cannot absolutely produce it. It probably acts by keeping up 
a constant irritation in the alimentary canal, thus causing 
diarrhoea, which in cholera epidemics usually precedes the 
outbreak of the graver disease. 

408. Malarious Fevers. — There is strong evidence in sup- 
port of the belief that these are often produced by drinking 
marsh or ditch water. They are supposed to be caused by 
some specific poison generated in marshy regions ; and that 
this may find its way into the blood through the agency of 
water, as well as of air, there is no reason to doubt. Mr. 
Blower, of Bedford, England, mentions a case in which, in the 
parish of Houghton, almost the only family which escaped 
ague at one time was that of a farmer who used well-water, 
while all the other inhabitants drank ditch-water. 

Numerous instances point to impure water as a frequent 
source of typhoid fever. Doubtless, water contaminated by 
decomposing sewage, or evacuations from typhoid patients, not 
only predisposes to the disease, but conveys its specific poison. 

In yellow fever, like dysentery, typhoid fever, and cholera, 
the alimentary mucous membrane is primarily affected. Hence, 
there is strong probability that the cause is also swallowed in 
this case, and enters with the drinking-water. 

409. Goitre, or enlargement of the thyroid gland, is most 
common in limestone regions, and is held by some to be caused 
by drinking water highly impregnated with lime and magnesia 
salts. Johnston states that in the jail at Durham, England, 
when the water contained 77 grains per gallon of lime and 
magnesia salts, all the prisoners had swellings of the neck. 
These disappeared when a purer water, containing 18 grains 
per gallon, was obtained. 

410. Entozoa, or those parasitical creatures which infest 
other animals, may find their way into the body by means of 
the drinking-water. While some ^nter with the food, others 
(in the embryo state) are known to exist in great numbers in 
river-water, and doubtless are often swallowed when such 
water is used for drinking purposes. 



306 ELEMENTARY HYGIEIs^E. 

Section IV. — Purification of Water, 

411. Examination by the Senses. — If water is examined 
by the unaided senses, the information obtained is very limited 
and should not be relied upon. They will only indicate ex- 
treme conditions, and are very liable to overlook the most 
characteristic impurities. Taste, for instance, even though it 
be extremely delicate, is wholly untrustworthy. Organic mat- 
ter, when dissolved, is often quite tasteless ; 55 grains of car- 
bonate of soda and 70 of chloride of sodium per gallon are 
imperceptible; 16 grains of carbonate of lime give no taste, 
and 25 grains of sulphate of lime very little. If, from its 
effects, a given water is suspected of impurity, and its use can- 
not be avoided, examination of it should be intrusted to some 
competent person. 

412. Distillation. — Water may be most thoroughly puri- 
fied by distillation, but this is impracticable when considerable 
quantities are required, and besides, the water is not fit to drink 
until aerated. To render it perfectly pure, it must be redis- 
tilled at low temperatures, in silver vessels. 

413. Boiling and Preezing. — ^Boiling kills most animal 
and vegetable organisms that water may contain, expels gases, 
and precipitates carbonate of lime. It is the latter that consti- 
tutes the fur or crust often seen lining tea-kettles and boilers. 

Freezing renders water much purer, by expelling a large 
proportion of its saline contents. Carbonate and sulphate of 
lime may be thus got rid of. But, like boiling and distillation, 
freezing expels the air and thus renders the water insipid. In 
all these cases the water regains its palatability on standing. 

414. Purification by Chemical Means. — The addition of 
two or three grains of alum to the quart cleanses muddy or 
turbid water, but often renders it harder than before. When 
alum is added, the water should not be used under 24 hours. 
Permanganate of potash destroys organic matter and ammo- 
niacal compounds by rapid oxidation, and may be used with 
advantage for this purpose. 



PUEIFICATION OF WATER. 307 

415. Filtration. — This is the most effective and practicable 
method of purification, and is within the reach of every one. 
Many substances will answer as filters, such as crushed char- 
coal, sand, or porous sandstone, flannel, wool, sponges, or any 
other porous media. Of all these, charcoal is the best. It will 
remove 88 per cent, of organic matter, and 28 per cent, of min- 
eral matters. If the Vv^ater is moderately good, 1 pound of 
charcoal will purify 600 pounds or 60 gallons. Animal char- 
coal is better than vegetable, though both lose their purifying 
power sooner or later. It is quietly restored, however, by ex- 
posure to air and slight heat. Filters of charcoal should be 
made of considerable thickness, and the coal finely crushed and 
well pressed together. The effect of the charcoal is supposed 
to be chiefly chemical, as it brings the large quantity of oxygen 
which it holds into the closest contact with any oxidizable mat- 
ters in the water. 

Sand is much used, and answers well for a time, but re- 
quires to be often renewed. 

416. Action of Water on Lead. — Water is known to pos- 
sess the power of corroding lead, and forming compounds with 
it which, if dissolved, render the water highly poisonous. All 
waters act upon it more or less, but it is only when the lead is 
dissolved that the water containins: it becomes dano-erous. 
When ordinary water is placed in contact with lead, the free 
oxygen it contains combines with the metal, forming oxide of 
lead, with which the water immediately unites, producing hy- 
drated oxide of lead, which is nearly insoluble. There is also 
more or less carbonic acid existing in all natural waters ; this 
combines with the oxide of lead, forming carbonate of lead, 
which is also highly insoluble. But if there be in the water 
much carbonic acid, a bicarbonate of lead is formed, which is 
very soluble, and therefore remains dissolved in the water. 
Hence, waters which abound in free carbonic acid, as also 
those which contain bicarbonates of linio, maoiiesia, and yoi- 
ash, are most liable to become poisoned by lead. AVater con- 
taining common salt acts upon the metal, forming a soluble 



308 ELEMENTARY HYGIENE. 

poisonous chloride of lead. The presence of organic matter, 
nitrites and nitrates, imparts to the water a powerfully corrosive 
action. If the water contains vegetable or fatty acids of any- 
kind, or sour milk, or cider, its action on lead is greatly in- 
creased, and it is more likely to dissolve the compounds formed. 
On the other hand, waters containing sulphates and phosphates 
are little injured, these salts exerting a protective influence on 
the lead. 

The lead itself is more easily acted upon if other metals, 
such as iron, zinc, or tin, are in contact with it. Galvanic ac- 
tion is set up, which greatly facilitates corrosion. 

Dr. Hassal says that *' while very soft water cannot he 
stored for a lengthened period, with impunity, in leaden ves- 
sels, the danger of the storage of hard water, under the same 
circumstances, is in most cases much greater. This danger, 
however, is to be estimated neither by the qualities of hard- 
ness or softness, but altogether depends upon the chemical 
constitution of each different kind of water. Thus, if this be 
ever so soft, and contain free carbonic acid, its action on lead 
will be great ; whereas, if it be hard from the presence of sul- 
phates and phosphates principally, and contain but few bicar- 
bonates, little or no solution of the lead will result." 



CHAPTER XVII. 

FOOD AND HEALTH. 

Section I. — The Alimentary Principles of Food. 

417. The Four Groups. — It was stated in Chapter VII., 
Section L, that all substances used as foods may be classed 
under four heads, either as Proteids, Fats, Amyloids, or Min- 
erals. It is desirable to recapitulate and somewhat extend the 
observations there made. 



THE ALIMENTARY PKINCIPLES OF FOOD. 309 

418. The Proteids. — This group of alimentary principles 
consists of Gluten, Fibrin, Albumen, Syntonin, Casein, and 
Gelatin, whicli are cbaracterized by the presence in their com- 
position of a large amount of nitrogen. 

Gluten is the adhesive principle of grain, and is a grayish, 
tough, elastic substance, left when the starch is thoroughly 
washed away from flour. From its resemblance to the fibrous 
part of meat, it is known as vegetable fibrin. Animal fibrin 
exists dissolved in the blood, and solidifies into a fine net-work 
as the blood coaoculates. It constitutes the bulk of lean meat. 
Casein is the curdy principle of milk, which is separated by 
coagulation, and forms the chief ingredient of cheese. It ex- 
ists in large quantity (20 to 28 per cent.) in beans and peas, 
and is known as vegetable casein. Albumen is a transparent, 
glairy, coagulable fluid, familiar to all as white of egg. It is 
a large constituent of animal fluids and tissues, and occurs in 
the seeds and juices of plants. Syntonin is the chief constitu- 
ent of muscle or flesh. It closely resembles albumen in com- 
position, but, unlike it, is not a product of the vegetable king- 
dom. Gelatin is an animal product, chiefly obtained from 
bones and tendons. It is not found in the vegetable kingdom, 
and is used for food, principally in the form of jellies and 
soups. 

All the foregoing substances, except gelatin, have a re- 
markable similarity of composition. They present varieties of 
aspect and physical properties, and differ in consistency, solu- 
bility, and behavior with heat ; but they serve a common pur- 
pose in the animal economy — that of furnishing material for 
the formation of the tissues — and on this account have a high 
nutritive value, and arc to a great extent mutually replaceable. 

419. The Fats. — These occur in both plants and animals, 
and, whatever their source, they have a great similarity of com- 
position. Like the proteids, they differ in physical properties, 
but are capable of replacing each other as articles of diet. 
They are essential to the formation of both muscular and ner- 
vous tissue, and, from their large amount of h} drogen and car- 



310 ELEMENTARY HYGIENE. 

bon, are the most energetic supporters of tlie calorifying 
function. 

420. The Amyloids. — This group comprises the starches, 
sugars, and gums — principally vegetable products, and, in one 
form or another, is a large constituent of our ordinary food. 
Starch is abundant in grain, peas, beans, and potatoes. The dif- 
ferent preparations known as sago, tapioca, arrow-root, and the 
like, are almost entirely starch extracted from different species of 
plants. Starch is capable of conversion into sugar, and is thus 
changed by the juices of the alimentary canal. Sugar is pro- 
duced by both plants and animals, but our supply comes chiefly 
from the vegetable kingdom, where it is contained in great 
abundance in sap, fruit, and seeds. By the agency of heat, 
starch may be converted into gum, known as dextrine. Gums 
are vegetable products widely distributed, but not in great 
abundance. Their composition is similar to that of starch and 
sugar, and their dietetical function is supposed to be the same. 

421. Their Offices. — It has until lately been supposed that 
as the nitrogenous and non-nitrogenous substances are clearly 
separated by chemical compositions, they are sharply divided 
in their physiological effects. The first were supposed to nour- 
ish the tissues, the decomposition of which was believed to be 
the sole source of animal power, while the fatty and amyloid 
group served only to maintain animal heat by their oxidation. 
Bat while it is maintained that the bodily tissues can only be 
reproduced from the nitrogenous elements, it is admitted that 
the decomposition of these tissues must be a source of heat; 
and recent researches have established that the combustion 
of the hydro-carbons is a source of power, the heat produced 
being converted into mechanical force. 

422. Mineral Aliments. — The inorganic or mineral con- 
stituents of food consist of water and various saline substances. 
Common salt occurs in all forms of food, but in larger propor- 
tion in animal than in vegetable tissues. An instinctive crav- 
ing impels animals to seek for a larger supply of it than is fur- 
nished in their food. Chloride of potassium, phosphate of lime, 



THE ALIMENTARY PRINCIPLES OF FOOD. 311 

and alkaline carbonates are indispensable to digestion, and are 
fiirnisbed in combination with the various aliments. 

423. Necessity for a Mixed Diet. — The usual forms of 
food are combinations of these alimentary principles. Milk, 
for example, is a highly complex animal product, containing 
water, casein, butter, sugar, and various mineral salts — repre- 
sentatives of each of the four classes of alimentary principles. 
By its excess of salts and nitrogenous matter, it is suited to the 
wants of the infant, or rapidly growing state of the constitution, 
but it is not a complete or properly balanced diet for the adult. 
In the majority of cases, no single article of food is thus com- 
plete in its composition, there being usually one or more of the 
essential elements of a perfect diet wanting. This is the case 
with the various meats, all of which abound in nitrogenous and 
fatty substances, but are deficient in the amyloid elements. 
On the other hand, most vegetables are rich in starch and 
sugar, but deficient in nitrogenous matters. Bread is nitroge- 
nous, amylaceous, and inorganic, but lacks fat ; while Indian 
corn contains less of the nitrogenous element, but a large 
amount of starch and 8 or 10 per cent, of fat. As no one arti- 
cle of food, therefore, contains these four classes of materials 
in the proportions requisite to a perfect diet, we are obliged to 
mix our various food-stufls. Confinement to a single aliment- 
ary principle, or to any one class of them alone, is sure to be 
followed by disease. It has been shown, by repeated experi- 
ments, that dogs confined to the exclusive use of either starch, 
fat, or albumen, soon die of starvation. Like experiments be- 
gun upon men were productive of a corresponding disturbance, 
and doubtless, if carried out, would have resulted in the same 
way. 

The proteids are first in importance, as much the larger 
part of the mass of the body is derived from them, and, when 
given alone, will sustain its powers longer than any other class 
of aliments. Hence, it is easy to see why exhaustion follows so 
much more quickly when they are withheld, than when other 
kinds of food are unsupplied. But the amyloids and tats are 



312 ELEMENTARY HYGIENE. 

also requisite, and the body feels the want of them sooner or 
later, even though the proteids are furnished in abundance. 

Section II. — Animal Foods, 

Foods may be conveniently divided into three classes : 
animal food, vegetable food, and auxiliary food ; substances 
derived from animals, such as milk, eggs, and meats, are ex- 
amples of the first class. 

424. Milk. — As this liquid contains all the elements ne- 
cessary for complete nutrition, it has been regarded as the type 
of composite foods, but, as just remarked, it is only completely 
adapted to a certain stage of animal life. A hundred parts of 
cow's milk contain of casein, 4.48; of butter, 3.13 ; of milk- 
sugar, 4.47 ; salts, .60 ; and of water, 87.32. This, however, 
is only an average statement, as no two cows give milk exactly 
alike in composition, while the milk of the same cow varies 
with the food. The milk of goats and ewes is richer in solids 
than that of the cow. Human milk is poorer in casein, and 
contains a larger proportion of sugar than cow's milk ; hence, 
when the latter is substituted for it in the case of infants, a lit- 
tle sugar should be added. 

In cities, milk is often largely adulterated with water. If 
much water has been added, it may be detected by applying 
the specific gravity test. The specific gravity of unadulterated 
milk ranges from 1.026 to 1.033 ; the average is about 1.030. 
Two-parts water to eight-parts milk will reduce its specific 
gravity to 1.024; four-parts water to six-parts milk, to 1.018. 
Good milk should be of a full white color, perfectly opaque, 
without deposit, and free from any peculiar taste or smell. It 
should give a neutral reaction, and have a specific gravity of at 
least 1.028. 

425. Butter and Cheese. — These furnish the nutritive con- 
stituents of milk in a concentrated form. Butter is habitually 
associated with substances which are deficient in fat, and is 
held to promote their digestibility. All butter contains casein. 



ANIMAL FOODS. 313 

which is derived from the milk sldmmed off with the cream, 
but the less it contains the less liable it is to become rancid. 
Rancidity is chiefly owino; to changes in the oil produced by 
decomposition of the casein. Butter in this condition is unfit 
for food, as it is indigestible, and has been known to produce 
dyspepsia and diarrhcea. Cheese is rich in nitrogenous mate- 
rial, and when fresh is regarded as excellent food. It is very 
liable, however, to undergo chemical change, and when this is 
once set up it becomes irritating and indigestible. The pecu- 
liar flavor of old cheese arises from this commencing decompo- 
sition, and it often disturbs weak stomachs. In this condition 
it is said to aid digestion, and is sometimes taken in small 
quantities as a condiment. 

426. Eggs. — These are both nitrogenous and fatty, and, 
when properly cooked, are easily digested and highly nutri- 
tious. They contain no starch or sugar, and should therefore 
be eaten in connection with such articles as supply these ali- 
ments. Eggs are most wholesome when boiled sufficiently to 
coagulate the white without hardening the yolk. Hard-boiled 
or fried eggs digest with difficulty. 

427. Meats. — Whatever their source, these are essentially 
tlie same in constitution, that is, they all contain a large amount 
of nitrogenous matter, in union with much fat and various im- 
portant salts. Their advantage as a diet is, that they contain 
a large amount of nutriment in a highly concentrated form, are 
easily digested when properly cooked, and admit of ready 
assimilation. 

Fresh meat varies in quality with diflercnt animal?, and 
with the age, sex, and condition of the individual from which 
it was obtained, as well as with the character of the food upon 
which it was fattened. Stall-fed cattle make the finest beef, 
and corn-fed swine the best pork. The nicest mutton is ob- 
tained from sheep fattened on fresh, succulent pasturage. In 
all cases the animal should be free from disease, and of medium 
fcitness, to make its flesh a healthy and economical food. The 
muscle should be of a firm, yet not sodden, consistence, of a 
14 



314 ELEMENTARY HYGIENE. 

pale-redclish color, somewhat lighter toward the centre than at 
the surface, and show no disposition to tear across its fibres. 
The fat should be white, or but slightly tinged with yellow, 
and also firm to the touch. The pale, moist muscle marks the 
young animal ; the dark colored, the old one. The meat 
should be free from any disagreeable odor, and the muscles, 
when cut across, should present a uniform solidity. Any mar- 
bling, or points where the knife passes more easily than at 
others, indicates commencing decomposition. As a rule, the 
flesh of young animals is tenderer, and more easily digested 
than that of old ones ; veal, however, is an exception, so far as 
digestibility is concerned. The flesh of young animals contains 
more water than that of old ones, consequently it is more 
juicy, but bulk for bulk less nutritious. 

428. Salt Meat. — Beef and pork are commonly preserved 
for future use by salting, and in this condition are largely em- 
ployed as food. Salting, however, reduces the nutritious value 
of meat, detracts from its flavor, and renders its digestion more 
difficult. It does this by extracting a portion of its juices, 
which remain dissolved in the brine, thus leaving the fibres of 
the meat harder and consequently less easily acted upon by the 
fluids of the stomach. 

429. Poultry and Game. — Meat of this kind is more easily 
digested than that just considered, but is regarded as less nu- 
tritious. It is not so juicy as butcher's meat, and, as a rule, 
contains less fat. Broths made from it have a delicate flavor, 
and contain considerable nutriment, hence they make an excel- 
lent food for convalescents. 

430. Pish. — The flesh of fish is very similar in composition 
to that of other animals. It is somewhat poorer in nitrogenous 
matter, but richer in important salts, and contains a higher pro- 
portion of water than butcher's meat. 

It is generally of easy digestion, but it should not be used 
exclusively, nor for a long period together, as it is liable to 
produce a scorbutic state of the system. The flesh of fish un- 
dergoes rapid decomposition, and is then highly injurious. It 



VEGETABLE FOOD. 315 

should be eaten only when it is perfectly fresh. Salt fish, like 
salt beef or pork, is much inferior to fresh, and extremely in- 
digestible. 

431. Crabs and Lobsters. — The flesh of these animals re- 
sembles that of fish, but it is less easily digested. It is pe- 
culiarly prone to decomposition, and, when eaten in this state, 
often produces sickness and sometimes proves fatal. 

432. Clams and Oysters. — Clams, either raw or cooked, 
are extremely indigestible. Oysters are much less so. They 
are most easily digested when raw, and, if cooked, should be 
either stewed or roasted. 



Section III. — Vegetable Food. 

433. Wheat. — Of vegetable food-stuffs, the most important 
and widely-used are the cereal grains. Among these wheat 
ranks first, both in point of nutritive value and in the ease with 
which it is digested. With the exception of milk, it approaches 
more nearly the standard of a perfect food, and will sustain the 
powers of the body for a longer period than any other article 
of diet. It contains from 10 to 15 per cent, of gluten; from 
60 to 70 per cent, of starchy matter, and a small proportion of 
fat, besides certain important alkaline and earthy phosphates. 
Its proportion of water is very low, averaging about 12 per 
cent., bulk for bulk ; therefore it is richer in solids than any 
other food. The starchy elements of the seed exist most 
abundantly in and about its centre, while its glutinous, flitty, 
and mineral constituents are found in greatest quantity toward 
the surface. The coat immediately beneath the husk is espe- 
cially rich in gluten, and therefore highly valuable as food. In 
the process of grinding, this is often lost by passing into the 
bran, the result being a whiter, but much less nutritious tlour. 
The soft wheats yield the whitest flours, as they contain more 
starch and less gluten than the hard or flinty varieties. Good 
wheat should yield at least 80 per cent, of flour. 

The quality of wheaten flour may be best determined by the 



316 ELEMENTARY HYGIENE. 

practical test of baking. Still something may be told by its 
appearance. It should contain very little bran, and its starch 
should be white, or with the very slightest tinge of yellow. 
The flour ought not to be lumpy, or if so, the lumps should 
readily give way under the slightest pressure. Grittiness in- 
dicates that the starch-grains are changing, and such flour will 
give an acid bread. AVhen compressed in the hand, good flour 
will adhere in a lump, and retain the imprints of the fingers 
longer than that of inferior grade. If cast against the wall, a 
portion should firmly adhere. The dough made with good 
flour is ductile and elastic, and may be drawn out into long 
strips, or rolled into thin sheets without breaking. 

Flour becomes whiter with age, but it is at the expense of 
flavor, sweetness, and nutritive value. The greater the propor- 
tion of gluten, the sooner will this deterioration take place. 
Flour is sometimes contaminated by the presence of fungi or 
insects, and they always indicate inferior quality. It is also 
occasionally adulterated with the flour of other grains, which 
can only be detected by the microscope. 

434. Eye. — This comes next to wheat in nutritive value, 
though it furnishes less flour to the bushel, and that of a de- 
cidedly darker color. Its gluten appears to contain more 
casein and less vegetable fibrin than that of wheat, conse- 
quently it is less tenacious. Owing to this quality, bread made 
from rye flour does not rise well, and is liable to become heavy 
on cooling. Rye bread soon becomes acid, and with many is 
not easily digested. 

435. Buckwheat. — This is poor in nitrogenous and fatty 
constituents, but rich in starch. Bread made from buckwheat 
flour does not rise well, owing to its deficiency in gluten. It 
is, therefore, chiefly consumed in making griddle-cakes, which, 
while warm, are light and palatable, but not well received by 
weak stomachs. 

436. Indian Corn contains a much larger proportion of 
fat than any other grain in common use. It is also rich in 
starch, but has far less nitrogenous matter than either wheat 



VEGETABLE FOOD. 8lY 

or rye. This, which is known as zein, is not of a glutinous, 
adhesive nature, and hence maize flour, or meal, will not make 
a dough, or fermented bread. In the preparation of articles of 
food from Indian meal, long cooking is necessary, when it 
makes both a palatable and highly nutritious food, which is 
easily digested. 

437. Rice. — As an article of diet, rice possesses the advan- 
tage of an extremely digestible starch-grain. It has, however, 
but small proportions of nitrogenous matter, fat, and salts ; 
hence, in rice-eating nations, it is habitually taken with such 
other food as will best supply these wants. 

438. Peas and Beans are much alike in composition, and 
both rich in nitrogenous constituents, often containing as high 
as 26 per cent, of vegetable casein, or legumen. They also 
contain much sulphur and phosphorus, together with an aver- 
age proportion of salts, and but a small quantity of water. 
They are, therefore, very nutritious, and rank first anaong con- 
centrated strength-imparting foods. They are somewhat indi- 
gestible, however, and liable to produce flatus. When eaten, 
it should be in small quantity, and only by those of an active 
habit of body. 

439. Succulent Vegetables. — Of these, potatoes are the 
most valuable and most extensively used. They contain in 
100 parts- 
Water, 14: 

Proteids, 1.5 

Fats, ...... .1 

Amyloids, , 23.4 

Salts, 1 

They are thus seen to abound in amylaceous materials and salts, 
but contain a low proportion of nitrogenous matters, and very 
little fat. Owing to this deficiency, we habitually associate 
them with meat, when they form an easily-digested and valu- 
able food. 

Turnips, beets, carrots, parsnips, etc., contain more water 
than potatoes, and are less easily digested. Their solid por- 



318 ELEMENTARY HYGIENE. 

tions consist mainly of starch and sugar, with a small percent- 
age of fat and salts. They each possess a peculiar, volatile 
principle, which adds much to their flavor, and causes them to 
be eaten more as a relish than as a strength-giving food. 

Onions and cabbage are more watery than the preceding, 
but their solid parts contain a very large proportion of nitro- 
genous matter. They are relished chiefly for their pungency, 
but should be eaten only at intervals, as they are likely to 
cause flatus and indigestion. 

440. The Fruits. — These consist mostly of water and cel- 
lulose, with varying amounts of fruit sugar, and small quantities 
of potash, soda, and lime, in combination with certain organic 
acids. Their juices contain a gelatinous substance termed, 
pectine, v/hich forms the basis of the various jellies. Fruits 
are prized more for those qualities which relate to their taste 
than for nourishing and strengthening power. Nevertheless, 
they are valuable as sources of the alkaline and earthy carbo- 
nates, and useful when eaten in moderate quantity, as safe- 
guards against constipation. They are most wholesome when 
cooked, but in all cases the skins, seeds, and cores should be 
rejected, as indigestible and prolific sources of irritation. 

Section IV. — Auxiliary Foods, 

441. Auxiliary foods comprise a class of substances very 
extensively employed to give relish to other dietary compounds, 
to provoke the digestive organs, and for nervous stimulation, 
rather than for any nutritive properties of their own. Useful 
when taken with care, they are liable to prove most injurious 
when too freely indulged in. Under this head come the 
various condiments and beverages. 

442. The Condiments. — Vinegar is essentially a solution 
of acetic acid in w^ater. Good vinegar ought to contain at least 
5 per cent, of the acid. Commercial vinegar is often largely 
adulterated, and some samples which pass under the name are 
made of sulphuric acid and water, colored wdth burnt sugar, 



AUXILIARY FOODS. 319 

and without a trace of acetic acid in their composition. Vine- 
gar in small quantities, by augmenting the acidity of the 
stomach, may reenforce the gastric juice, and promote the di- 
gestion of the proteids. 

Black pepper consists of an active principle [peperin)^ a 
pungent essential oil, and an acrid resin. It is a powerful 
stimulant of the digestive organs, increasing the flow of saliva 
and gastric juice in a marked degree. In the powdered state 
it is frequently adulterated with linseed meal, starch, mustard, 
buckwheat bran, etc. These may be detected by the micro- 
scope ; but it is safest to purchase the berries and grind them 
as wanted. 

Cayenne pepper resembles black pepper in properties, but 
is a much more powerful stimulant. Its habitual use, there- 
fore, cannot be recommended, and if taken at all, it should be 
only in the smallest quantity. 

The sharp, acrid smell and taste of mustard are due to the 
volatile oil it contains. Used in small quantities, it is a gentle 
stimulant ; in large doses, it acts as an emetic. Like all arti- 
cles of its class, it is subject to sophistication. Among the 
substances added, the most common are turmeric and some 
form of starch. Sulphate of lime and chalk are also sometimes 
used as adulterants. 

443. Beverages.— Tea.— This consists of the leaves of the 
tea-shrub, grown and prepared chiefly in China. Many vari- 
eties are known in commerce, the differences between which 
are due probably to diftcrent modes of culture and prepara- 
tion. 

The substances for wdiich tea is most prized as a beverao-e 
are—Jirstj a peculiar volatile oil, which gives the tea its agree- 
able flavor; second, a vegetable alkali, rich in nitrogen, and 
known as thein, — the active principle of tea; and third, tannic 
acid, which gives the tea its astringent quality. Of the fii-st, 
tea contains less than 1 per cent. ; of the second, tVoui l^V to G 
per cent. ; and of the tannic acid, wdiich is in combination with 
the thein, from 14 to 16 per cent. It contains, besides, about 



320 ELEMENTATJY HYGIENE. 

20 per cent, of gluten, and is also ricli in salts, but these last 
ingredients are not usually obtained in the beverage. 

In making tea, it is desirable to obtain from the leaves the 
largest possible amount of matter, without destroying its flavor. 
If the tea is boiled, the volatile oil is driven off with the steam 
— and yet a boiling temperature is required to dissolve the 
compound of thein and tannic acid, the most important con- 
stituent of the leaf. To preserve the one and obtain the other 
is the principal object, and this is best attained by pouring 
boiling water upon the leaves in close vessels, and allowing 
them to steep for a time, with the temperature slightly below 
the boiling point. 

Tea acts as a gentle stimulant upon the nervous system, 
without producing subsequent perceptible depression. It also 
quickens the pulse somewhat, and increases the amount of pul- 
monary carbonic acid exhaled. It produces an astringent effect 
upon the bowels, but not to any harmful extent. It hastens 
digestion and is invigorating, but it should not be taken in 
excess, as it is apt to induce wakefulness and an irritable state 
of the system. Green tea is more injurious in this respect 
than black, often giving rise to nervous tremors. 

Tea of all sorts is liable to the grossest adulteration, green 
teas being worse in this respect than the black varieties. The 
Chinese heighten their color, or face them, as it is termed, by 
the addition of Prussian blue, indigo, turmeric, gypsum, and 
China clay. A bright-green color is to be looked upon with 
suspicion, as the pure article always presents a dull, faded 
green appearance. The leaves of other plants are often mixed 
with tea. Sometimes, also, exhausted tea leaves or grounds 
are bought up, their astringent property restored by the addi- 
tion of catechu, and colored with black lead, or logwood, they 
are sold again as genuine tea. Another fraud of great preva- 
lence consists in mixing inferior qualities of tea with better 
sorts, and cheating the purchaser by selhng the compound at 
the price of the best article. 

In selecting tea, it should appear not to be too much 



AUXILIARY FOODS. 321 

broken up, or mixed with dirt, smd the leaves should vary 
somewhat in size and color. The best teas contain portions 
of the stalk and flower. Old teas do not possess so rich a 
flavor as fresh, owing to the loss of a portion of their vola- 
tile oil. 

444. Coffee. — Coffee, hke tea, contains a volatile oil, a ve- 
getable alkali (caffein)^ and tannic acid. It also contains from 
12 to 15 per cent, of amylaceous material, in the shape of 
sugar and gum, and nearly the same quantity of nitrogenous 
matter, in various forms, besides being rich in salts. But veiy 
small quantities of these latter substances find their way into 
the beverage. 

The agreeable flavor of coffee is due to its volatile oil, which 
is present in very minute proportions, and requires the action 
of heat to develop it. This is done by the process of torrefying. 
The caflein is almost identical in composition with the thein 
of tea, and, like it, is the active principle of the beverage. It 
is present in small quantity, rarely reaching 1 per cent. The 
quantity of tannic acid is usually less than 6 per cent., conse- 
quently coffee is much less astringent than tea. 

The action of coffee upon the system is similar to that of 
tea. It is a stimulant, and promotes the digestion and assimi- 
lation of food. It both enlivens the mind and invigorates the 
body, relieving the depression of fatigue, and in this way un- 
doubtedly tends to diminish the liability to disease. 

There is a peculiar physiological effect exerted by coff*ee 
and tea, and probably also by alcoholic beverages when taken 
in small amount — a retardation of destructive metamorphosis. 
The renal products of muscular w^aste are found to be dimin- 
ished after their use; while experience has shown that they 
may replace, in diet, a certain amount of ordinary food. Pe 
Gasparin, in his observations upon the regimen of the Belgian 
miners, found that *Hhe addition of a quantity of cotVoe to the 
daily rations enabled them to perform their arduous labors on 
a diet wdiich was even below that found necessary in prisons 
and elsewhere, wdiere the article was not employed.'" The 
14-^' 



322 ELEMENTARY HYGIENE. 

comparative effects of coffee, tea, and alcohol, in enabling men 
to endure cold and hardship, are thus stated by Dr. Hayes, in 
describing the experiences of Arctic exploration : "Dr. Kane's 
parties, after repeated trial, took most kindly to coffee in the 
morning, and tea in the evening. The coffee seemed to last 
throughout the day, and the men seemed to grow hungry less 
rapidly after taking it than after drinking tea, while tea soothed 
them after a day's hard labor, and the better enabled them to 
sleep. They both operated upon fatigued and over-taxed men 
like a charm, and their superiority over alcoholic stimulants 
was very marked." 

In the process of roasting, the coffee should be first care- 
fully dried in an open pan, over a gentle fire, until it becomes 
yellow. It should then be scorched in a covered vessel, to pre- 
vent the escape of aroma, taking care, by proper agitation, to 
prevent any portion from being burnt, as a few charred grains 
communicate a bad odor to the rest. The operation should be 
continued until the coffee acquires a deep cinnamon or chest- 
nut color, and an oily appearance, or until the peculiar fra- 
grance of roasted coffee is sufi[iciently strong. Unroasted coffee 
may be kept for any length of time, and grows better with age. 
After roasting, it is constantly losing flavor; hence, it is well 
to roast but a small quantity at once, and this ought to be 
kept in close vessels, and ground as it is wanted for use. This 
course necessitates the purchase of the berry and home pre- 
paration, but the additional trouble is more than compen- 
sated by the superior beverage thus obtained. The finer it 
is ground, the more readily, of course, will it yield its soluble 
constituents. 

Ground coffee is very extensively adulterated ; — ^hence an- 
other inducement for purchasing the whole berries. Various 
substances are employed as adulterants, such as roasted peas, 
beans, corn, turnips, carrots, potatoes, etc. But the substance 
most commonly used is chiccory, which has a large white pars- 
nip-like root, abounding in a bitter juice. A little of this, 
when roasted, gives as dark a color and as bitter a taste to 



AUXILIARY FOODS. 323 

water as four times the quantity of coffee, and, as it only costs 
about one-third as much, the temptation is very strong to mix 
it with ground coffee. So great is the demand for chiccory for 
this purpose, that it is itself adulterated with roasted barley 
and wheat grains, acorns, mangel wurzel, sawdust, peas, and 
beans. Venetian red is sometimes added to give it a coffee 
color, and even this is cheapened by the addition of brick-dust. 
The microscope detects many of these foreign substances, 
while some can be identified only by chemical means. 

In the preparation of the beverage, we are met by the same 
difficulty that was encountered in the case of tea; that is, a 
high heat will drive off the aroma, while yet it is requisite to 
the extraction of the active principle — caffein. To obviate 
this difficulty, take two portions of coffee, boil the first for 
five minutes in the required amount of water ; then, after set- 
tling a moment, decant the water upon the second portion, and 
allow it to steep for a few moments y/ithout additional heat. 
Allow it to settle, pour off the liquor for use, and retain the 
grounds for the next day's boiling. A fresh portion furnishes 
the aroma, and can be in its turn subjected to the boiling 
process. 

445. Cocoa and Chocolate. — ^These are prepared from the 
cacao hearts, which are derived from a fruit resembling a short, 
thick cucumber, grown upon the small cacao-tree of the West 
Indies, Mexico, and South America. The bean is brittle, of a 
dark-brown color internally, and has a slightly astringent but 
decidedly bitter taste. In preparing it for use, it is roasted in 
the same way as coffee, until the aroma is fully developed. 
The bean is now more brittle, lighter in color, and less astrin- 
gent and bitter than before. The beans contain about 50 per 
cent, of fatty matter, called butter of cacao, and from 20 to 25 
per cent, of albuminous and starchy material. Thov also con- 
tain a peculiar nitrogenous substance called theohromln, similar 
in nature and properties to thein and caffoin. The boans, 
crushed to a })aste between hot rollers, and mixed with staivh, 
sugar, etc., form common cocoa. Chocolate is made by grind- 



324 ELEMENTARY HYGIENE. 

ing the recently-shelled beans to paste, mixing this with sugar, 
and flavoring it witli vanilla, cinnamon, and the like. When 
used as a beverage, the chocolate or cocoa is scraped into pow- 
der, mixed wdth water and milk, and brought to a boihng heat. 
As thus prepared, chocolate is refreshing to the spirits, and 
highly nutritious. 

Section Y. — Culinary Preparation of Foods. 

446. Cooking has a twofold object— /r^i^, to soften the 
food, and thus facilitate its solution in the digestive juices; 
and secondj to develop its flavor, and thus render it more 
agreeable to the palate. When the operation is properly per- 
formed, both these purposes may be attained, and yet by im- 
proper management both may be defeated. For example, in 
cooking meats, it is desirable to retain their flavor, preserve 
their juices, and soften their texture, and wdth the requisite 
care, all this may be accomplished ; yet how often does care- 
less or improper management give us a hard, dry, tasteless 
mass, as indigestible as it is unpalatable ! Over-cooking should 
be specially avoided, as it results in waste and loss of sapidity, 
without in any respect improving the character of the food. 

447. Cooking of Meats. — Boiling. — Meats lose from 25 
to 35 per cent, of their weight by this process. If it is desired 
to retain their juices and flavor, the pieces should be cut large, 
and when first put in, the v/ater should be boiling. This co- 
agulates the albumen near the surface of the piece, and thus 
prevents further escape. After boiling three or five minutes, 
the heat should be lowered to about 1G0°, and maintained at 
that point until the completion of the process. If the temper- 
ature is kept above 170°, the muscular tissue shrinks, and be- 
comes hard and indigestible. In making broth, the object is 
to extract the juices ; hence the meat should be cut into small 
pieces and placed in cold water. After standing a little time, 
it may be slowly heated to about 150° ; never much above this. 
CoagTilation of the albumen is thus prevented, and the con- 
tained juices extracted. A nutritious beef broth, or heef tea, 



CULINAEY PEEPAEATION OF FOODS. 325 

may be made without heat, by adding to a pint of cold water 
half a pound of finely-cut, fresh, lean beef and four or five 
drops of hydrochloric acid. Slight heat and a few drops more 
acid considerably increase the amount of extract. 

Roasting is one of the best methods of cooking meat. It 
not only develops the flavor, but preserves the juices, and 
leaves the meat in a condition to be easily digested. The loss 
is about 25 per cent., and is chiefly water. The process should 
be commenced with an intense heat, so as to coagulate the al- 
bumen of the surface and form a slight superficial crust. Af- 
terward it should be done very slowly, so as to avoid harden- 
ing the inner portions. 

Stewing is analogous to roasting, only the meat is cut up, 
and continually moistened with its own juices. Like boiling 
and roasting, it should be done at a low heat. Tough meat is 
best cooked in this manner. Baking requires to be conducted 
with great care, or there is danger of drying up the meat. 
Constant basting prevents this to some extent, but the method 
is inferior to roasting. Frying is the worst possible way in 
which meat can be cooked. The oil or fat requiring a high 
temperature to bring it to the boiling point, the meat is thus 
rendered extremely hard and the fat not unfrequently burnt. 
Broiling is to be preferred to frying. It has much the same 
effect as roasting, and, like that process, should not be carried 
too far — a high heat at first, sufificient to encrust the outside, 
and then a low temperature to complete the work. 

448. Cooking of Vegetables.— These are usually boiled, 
and are best cooked by this means. Care should be taken not 
to overdo them. Thorough softening is suflacient, as, when the 
process is carried beyond this, their structure is rapidly broken 
down, and a large proportion of their salts and juices lost in 
the water. The quality of the water employed exercises an 
important influence. Soft water exerts a much more poA\ orful 
extractive action than hard, hence food boiled in it is otten- 
times rendered insipid by the loss of its salts and juices. When 
it IS desirable to obtain these in a liquid form, as in niaking 



326 ELEMENTARY HYGIENE. 

soups, broths, or infusions, soft water is to be preferred. In 
' tbose cases where it is not the object to dissolve out the con- 
tents of a structure, but rather to preserve it firm and entire, 
hard water is the best. To prevent the over-dissolving action 
of soft water, salt is often added, and proves quite effectual. 

Section VI. — Injurious Effects of Bad Diet, 

449. Eflfects of Excess in Diet. — The influence of food 
upon health is immediate and powerful, and is manifested in 
various ways. Imperfect diet is chiefly injurious by its excess, 
by its deficiency, by the wrong proportions of its elements, 
and by the unwholesome condition of the articles consumed. 

The quantity of food that it is proper to take, varies, of 
course, with diff'erent circumstances : those thinly clad and 
exposed to cold require more than the well-protected ; those in 
active exercise more than the sedentary or persons of inactive 
habits ; while the growing need, proportionally to their size, 
more than adults. But whatever the circumstances, if the 
quantity of food taken exceed the demands of the system, evil 
consequences are certain to follow. The immediate results of 
over-eating are lethargy, heaviness, and tendency to sleep. 
Overtaxing of the digestive organs soon deranges their func- 
tions, and is a common and efficient cause of dyspepsia. If 
the food is not absorbed from the digestive apparatus into the 
system, it rapidly undergoes chemical decomposition in the 
alimentary canal, and often putrefies. Large quantities of gas 
are thus generated, which give rise to flatulence and colicky 
pain. Dyspepsia, constipation, and intestinal irritation, caus- 
ing diarrhoea which does not empty the bowels, are produced. 
If digestion be strong, and its products are absorbed, an excess 
of nutriment is thrown into the blood, and the circulation 
overloaded. If food is not expended in force, the natural 
alternative is its accumulation in the system, producing pleth- 
oric or abnormal increase of muscle, tissue, and fat. This 
is accompanied by congestion of important organs, mal-assimi- 



mJUEIOUS EFFECTS OF BAD DIET. 327 

lation of nutritive material, and increased proneness to derange- 
ment and diseased action. The excretory processes are like- 
wise certain to be disturbed, wbicli often leads to the retention 
of waste products, with perversion and poisoning of the blood, 
and a train of evil consequences. 

450. Effects of Deficient Diet. — As food is the source 
alike of the material organism and of the power it exerts, if a 
due supply of it is withheld, there is defective nutrition, which 
reduces the structures and impairs the strength. Habitual in- 
sufficiency of food lowers the vital powers and depresses the 
functions. There is loss of mental vigor and muscular energy, 
digestive disturbance, anaemia, and a tendency to those maladies 
which result from debility and undervitalized conditions. The 
resistance of the system to the numerous causes of disease is 
diminished : typhus and typhoid fevers are peculiarly diseases 
of the poorly-fed. In childhood, lack of sufficient food is often 
the cause of stunted growth and chronic disease, and in later 
life the parent of depraved appetites and moral perversities. 

Of the effects of stinted food upon mind and character. Dr. 
Moleshott observes : " There is another instinct by which the 
vigor of mind is vanquished iu a more melancholy way. Hun- 
ger desolates head and heart. Though the craving for nutri- 
ment may be lessened to a surprising degree during mental 
exertion, there exists nothing more hostile to the cheerfulness 
of an active, thoughtful mind, than the deprivation of liquid 
and solid food. To the starving man, every pressure becomes 
an intolerable burden ; for this reason, hunger has etieeted 
more revolutions than the ambition of disaffected subjects. It 
is not, then, the dictate of cupidity or the claim of idleness 
which prompts the belief in a natural human right to work 
and food." 

451. Amount of Food daily required. — Although this is 
variable in different circumstances, yet deiinite standards have 
been reached when dealing with large bodies of men in given 
cases. It has been shown that generally, in the ease o( the adnlt 
male, from ten to twelve ounces of carbon and from four to live 



328 ELEMENTARY HYGIENE. 

ounces of nitrogenizcd matter (estimated dry) are daily dis- 
charged from the organism, and that to replace this, there is 
required a daily consumption of from two to three pounds of 
solid food. Dr. Dalton says : " From experiments performed 
while living on an exclusive diet of bread, fish, meat, and 
butter, with coffee and water for drink, we have found that the 
entire quantity of food required during twenty-four hours, by a 
man in full health, and taking free exercise in the open air, is 
as follows : 

Meat, . . . .16 ounces, or I'OO lbs. avoirdupois. 
Bread, . . . 19 *' " 1-19 " '' 

Butter, or fat, . . SJ " ^' 022 '' " 

Water, ... 52 fluid oz. " 3-38 " " 

That is to say, rather less than two and a half pounds of solid 
food, and rather over three pints of liquid food." 

" It is undoubtedly true that the daily ration has frequently 
been diminished considerably below the physiological standard 
in charitable institutions, prisons, etc. ; but when there is com- 
plete inactivity of body and mind, this produces no other effect 
than that of slightly diminishing the weight and strength. The 
system then becomes reduced without any actual disease, and 
there is simply a diminished capacity for labor. But in the 
alimentation of large bodies of men subjected to exposure, and 
frequently called upon to perform great labor, the question of 
food is of vital importance, and the men collectively are like a 
powerful machine, in which a certain quantity of material must 
be furnished in order to produce the required amount of force. 
This important physiological fact is most strikingly exemplified 
in armies; and the history of the world presents few examples 
of warlike operations in which the efficiency of the men has 
not been impaired by insuflficient food. 

"The United States army-ration is the most generous in 
the world ; and the result has been that, in the recent civil 
war, scurvy and other diseases which are usually so rife in 
armies subject to the exposure and fatigue incident to grand 
military operations, have been comparatively rare. In some 



INJURIOUS EFFECTS OF BAD DIET. 329 

of the long and arduous campaigns of the war, the marches 
made by large bodies of troops, and the labor performed, 
showed an amount of endurance heretofore unknown in mili- 
tary history. The excellent physical condition of the men was 
further evidenced by the remarkable percentage of recoveries 
after serious wounds and surgical operations, and the slight 
prevalence of the ordinary diseases, except those of malarial 
origin."— (Dr. Flint.) 

The following is the army ration of the United States 
soldier : 

Bread or flour, 22 ounces. 

Fresh or salt beef (or pork or bacon, 12 oz.), . 20 '^ 
Potatoes (three times per week), . . . .16 *' 

Rice, 1-6 " 

Coffee (or tea, 0-24 oz.), 1*6 '^ 

Sugar, 24 " 

Beans, 0-64 gill. 

Vinegar, • . 0-32 "• 

Salt, 0-16 '' 

452. Effects of a badly-constituted Diet. — There may be 
sufficient bulkiness in the food taken, but such a misproportion 
among its elements as to pervert the functions and give rise to 
various maladies. The several elements of food-stufis are not 
replaceable. Deficiency of the proteids results in muscular 
debility and prostration ; while, if too great a quantity be 
taken, they charge the system with imperfectly-assimilated 
compounds and wrongly-changed products of decomposition, 
which produce a gouty state of the constitution. Deficiency 
of the fats induces defective nutrition and leanness ; while ex- 
cess of them not only tends to produce obesity, but if more 
be taken than can be stored or consumed, the burden of dis- 
posing of the excess falls upon the liver, which may itself be- 
come diseased from over-action, or its secretions be thrown 
into the blood, giving rise to a bilious condition of the system. 
If the saline elements are Avithheld, softening, or deformity of 
the bones, or rickets, is the legitimate consequence. If the 
supply of fresh vegetable food is cut off for a lengthened period, 



OOV ELEMENTARY HYGIENE. 

a scorbutic condition of body is produced. Hence, for the 
preservation of health, mixed food and a various, well-balanced 
diet are indispensable. 

In the case of infants and children, where food subserves 
the double purpose of maintaining activity and growth, 
there must be extra provision in the diet for the development 
of muscular and bony tissues. Milk, though a liquid, by its 
abundance of salts and casein, is adapted to this end. But too 
frequently, after weaning, the food of children is given with no 
reference to this important condition. Sago, tapioca, arrows- 
root, and jellies, vfhich rank lowest in nutritive value, with per- 
haps other substances less objectionable, but still inadequately 
nourishing, are frequently made use of, to the serious injury of 
the growing constitution. 

453. Effects of a Deficiency of Fat.— It is believed that 
a lack of oleaginous elements in diet predisposes to consump- 
tion. The immediate cause of this disease, as has been al- 
ready observed, is an abortive or perverted nutrition, tubercle 
being produced instead of healthy tissue. The seeds of con- 
sumption are most generally sown in the system in youth, 
when there is a double demand upon nutrition, for current 
waste and steady growth. There is, however, suflScient proteid 
matter present to nourish the structures ; some other condition 
must, therefore, be wanting. Eminent physiologists have lately 
maintained that the faulty nutrition w^hich results in tubercle 
is caused by a deficiency of oily substances, and therefore such 
of these bodies as are easiest digested and absorbed have been 
indicated as remedies. Cod-liver oil has come into use for this 
purpose. Dr. Hughes Bennett, who first introduced this oil to 
the notice of the public, states that butchers, cooks, oilmen, 
tanners, and others who are constantly coming in contact with 
fatty matter, are less liable than others to tubercular disease ; 
and Dr. Simpson has observed that children and young persons 
employed in wool factories, where large quantities of oil are 
daily used, are generally exempt from scrofula and pulmonary 
consumption. These facts would indicate that even the ab- 



USTJURIOUS EFFECTS OF BAD DIET. 331 

sorption of fatty matter through the skin may powerfully influ- 
ence nutrition. Dr. Bennett says that, to prevent consumption 
during youth, indulgence in indigestible articles of food should 
be avoided, especially pastry, unripe fruit, salted provisions, 
and acid drinks ; while the habit of eating a certain quantity 
of fat should be encouraged, and, if necessary, made imperative. 

Dr. Carpenter observes : " There is a strong tendency and 
increasing reason to believe that a deficiency of oleaginous 
matter, in a state fit for appropriating by the nutritive pro- 
cesses, is a fertile source of diseased action, especially that of a 
tuberculous character ; and that the habitual use of it in large 
proportions would operate favorably in the prevention of such 
maladies, as cod-liver oil unquestionably does in their cure." 

Dr. Hooker, in a report on the diet of the sick, says : " 1st. 
Of all persons between the ages of 15 and 22 years, more than 
one-fifth eat no fat meat. 2d. That of persons at the age of 
45, all except less than one in fifty habitually use fat meat. 
3d. Of those who have abstained, a few acquire an appetite 
for it, and live to a good old age, while the great proportion 
die of consumption before 45. 4th. Of persons dying of con- 
sumption between the ages of 15 and 45, nine-tenths, at least, 
have never used fat meat." 

454. Unwholesome Foods. — Articles of food difter in di- 
gestibility, some being readily dissolved and assimilated, while 
others are changed in the stomach with such difficulty as to 
irritate and injure the organ. Animal food is more easily 
digested than vegetable, as it represents vegetable food that 
has been already once digested, and its insoluble portions 
separated. But the chief cause of unwholesomeness in foods 
is their bad condition. The qualities which render them easily 
digestible within the system, make them readily changeable 
without it; hence their tendency to " spoil," and the facility 
of injurious culinary changes. Bread, sour and heavy from un- 
skilful working or damaged fiour, butter rancid and oflonsive, 
potatoes sodden, and meat tainted or diseased, are examples 
of unwholesome diet, which produce disturbance in tlie system 



332 ELEMENTARY HYGIENE. 

and often serious disease. Meat that has entered upon decora- 
position, or the flesh of diseased, immature, or over-driven 
animals, is unfit for use. They are liable to produce gastric 
disturbance and diarrhoea, or they may be actively and dan- 
gerously poisonous. 

455. Flesh Parasites. — The disease known as "measles" 
in the pig is due to little parasitic animals which infest the 
flesh. When pork is thus affected, there are found scattered 
through the areolar or connective tissues numerous opaque or 
-whitish points, which consist of little membranous bags, or 
cysts^ each containing a small embryonic animal, known as the 
Gysticercus cellulosus. These microscopic creatures are devel- 
oped from the eggs of the common tape-worm {Taenia solium). 

Dr. Kiichenmeister fed a number of cysticerci to a criminal 
at different periods before his execution, varying from 12 to 72 
hours, and, upon post-mortem examination of the body, no less 
than ten young tsenia were found in the intestine, four of which 
could be distinctly recognized as specimens of Tcenia solium 
(Dalton). 

The cysticerci are sometimes found in the organs of the 
human body as well as in those of the lower animals. They 
are most likely to be met with in the voluntary muscles, but 
have been observed in the tissue of the heart, and, what is 
more remarkable, in such organs as the eye and brain. Their 
presence in the muscles is not known to be harmful, inasmuch 
as they have been found in considerable numbers in those 
of individuals who were accidentally killed while in a state of 
apparently perfect health. 

The Trichina spiralis is another parasite which infests the 
muscles of the pig, and is also found in those of the human subject. 
A muscle containing trichina appears as if thickly beset with 
small whitish specks. Each speck is in reality a cyst, which 
contains a single trichinae, a minute, worm-like animal, coiled 
up in a spiral form. When straightened out, it measures about 
^^ of an inch in length, and about ^i-Q of an inch in diameter. 
Like the cysticerci, these animals find their way into the human 



INJURIOUS EFFECTS OF BAD DIET. 333 

stomach, and thence, by means of the circulation, to the mus- 
cles, where they are occasionally found in immense numbers. 
They have been discovered in the muscles of persons who died 
by accident, and were otherwise apparently healthy ; and also, 
and much more frequently, in subjects who have died from 
slow and debilitating disease. Within a few years past, it has 
been determined that the presence of these parasites not un- 
frequently gives rise to a peculiar disease, which has received 
the name of Trichiniasis, This affection is said to be highly 
febrile, often resembling typhoid or even typhus fever, and at- 
tended with excessive pain in the limbs and bowels. 

In selecting meat, if the lean flesh looks speckled or 
blotched, it should be suspected. "When the cysticerci are 
in great numbers, the flesh crackles as its fibres are cut across. 
The trichinae, if enclosed within a cyst, are easily seen with 
the naked eye ; but, if not, the microscope alone detects them. 
These creatures are said to be very tenacious of life, often sur- 
viving intense cold and a boiling heat. It is alleged, however, 
that thorough smoking effectually destroys them.- 



334 ELEMENTARY HYGIENE. 



CHAPTER XVIII. 

CLOTHING AND HEALTH. 

Section I. — Properties of Clothing Material. 

456. Purposes to be subserved. — The principal object of 
clothing being to defend the body against the effects of heat 
and cold, it is obvious that the qualities best suited to these 
purposes are what we are to seek in the selection of fabrics for 
wearing apparel in different seasons and climates, and at dif- 
ferent times. These qualities are chiefly connected with the 
relations of fabrics to heat and moisture. The body is con- 
stantly losing heat both by conduction and evaporation. In 
cold weather, the object is to prevent this loss as far as possi- 
ble ; in warm weather it is desirable to promote it ; hence, we 
select our clothing with a view to these different purposes, 
wearing the free conductors and ready absorbers in summer, 
and the non-conductors and slow absorbers in wdnter. As far 
as is consistent with these primary objects, clothing should be 
light, durable, and readily cleansed. It should also be of such 
a character as will allow of the free passage of the exhalations 
from the skin, and yet not be readily absorbent of moisture 
from without. Imperviousness is a very objectionable quality, 
and may, by retaining the cutaneous excretions in contact with 
the body, lead to serious disease. 

457. Linen as an Article of Clothing. — This is a good 
conductor, and allows the free escape of heat. It is also a 
rapid absorber of moisture, which it readily gives off by evapo- 
ration from the external surface of the body. For this reason, 
it produces a rapidly-cooling effect, even in hot weather, and 
is thus well adapted for summer use. It should not, however, 
under any circumstances, be worn next the skin, as it not only 
quickly cools the surface itself, but is incapable of preventing 
sudden chills from other causes. 



PEOPERTIES OF CLOTHING MATERIAL. 360 

458. Cotton as an Article of Clothing. — This is a worse 
conductor of heat than linen, and consequently warmer. It 
is likewise less absorbent of moisture, and is therefore prefer- 
able for under-garments, or when it is desirable to avoid the 
cooling action produced by the evaporation of moisture from a 
material in contact with the body. It ranks next to linen ara a 
fabric for summer wear, beiug a much better conductor of 
heat and absorber of moisture than either silk or wool. 

459. Woollen as an Article of Clothing. — Woollen fab- 
rics, owing to their coarseness and porosity, are capable of 
detaining within their meshes considerable amounts of atmos- 
pheric air, and this makes them bad conductors of heat. It 
is upon this property of imprisoning air within its interstices 
that the warmth of clothing in a great measure depends. The 
air itself is an excellent non-conductor of heat, and when mate- 
rials are worn which have the power of entrapping its particles, 
the body is virtually encased in a garment of air, and its heat 
thereby prevented from escaping. The denser the fibre and 
the closer the texture, the less air there will be retained, and, 
hence, the cooler the clothing. The converse is equally true, 
though to a more limited extent. In any clothing, if warmth 
is the object, the texture must be sufficiently close to prevent 
the passage of currents, but up to this point the more open it 
is, the better. 

Woollens also possess a great capacity for moisture, though 
they take it up and give it out very slowly. This is another 
valuable quality, giving them great advantages as articles of 
clothing. Every one may have noticed how readily linen and 
cotton become wet, while woollen in the same length of time 
is scarcely more than dampened. The former will also dry 
rapidly, while woollen parts with its moisture at a much slower 
rate. It is, therefore, a better protection ngainst wot than 
either linen or cotton, and much warmer while Avot, as the 
evaporation from its external surfiice is not nearly so rapid as 
from the surfaces of other materials. The water absorbed by 
different fabrics penetrates their fibres, and is also held between 



336 ELEMENTARY HYGIENE. 

them in the interstices of the cloth. The latter can be wrung 
out, and is called water of interposition. The former is only- 
got rid of by evaporation, and is termed hygroscopic water. 
Woollen greatly exceeds either linen or cotton in this power 
of hygroscopic absorption, taking up at least double the 
amount of water in proportion to its weight, and quadruple in 
proportion to its surface. 

^* This property is a most important one. During perspi- 
ration, the evaporation from the surface of the body is neces- 
sary to reduce the heat which is generated by exercise. When 
the exertion is finislied, evaporation still goes on, often to such 
an extent as to chill the frame. ^Taen dry woollen clothing is 
put on after exertion, the vapor from the surface of the body 
is condensed in the wool, and gives out again the large amount 
of heat which had become latent when the water w^as vaporized. 
Therefore, a woollen covering, from this cause alone, at once 
feels warm when used during sweating. In the case of cotton 
and linen, the perspiration passes through and evaporates from 
the external surface without condensation ; the loss of heat then 
continues. These facts make it plain why dry woollen clothes 
are so useful after exertion." — (Parkes.) 

As an equalizer of the temperature and protector of the 
surface against sudden chills, wool stands at the head of all our 
usual wearing fabrics, and, when it can be tolerated, should be 
constantly worn next the skin. 

460, Color influences the relations of clothing to solar heat, 
though it does not affect it in regard to non-luminous heat, 
such as that emitted from stoves. Black clothes absorb heat 
in a sunny day ; while white clothes reflect more of it. The 
power of absorption decreases as the shade grows lighter. 
Thus, black absorbs the most, blue next, then green, yellow, 
and lastly white. Color also aflects the relations of cloth to 
moisture, the darker colored materials absorbing more moisture 
than the light colored. Black will absorb nearly as much 
again as white. 



MANNER OF DEESSINa THE BODY. 337 

Section IL — Manner of Dressing the Body. 

461. Its Importance. — Much more depends upon this than 
upon the materials used. The best fabrics improperly put on 
may be the source of all sorts of diseases, while the poorest, if 
used with judgment, are capable of conferring a goodly degree 
of comfort. 

462. The Clothing should be Light. — All garments should 
be as light as is consistent with the main objects for which 
they are worn. Weight does not necessarily imply warmth, 
and it often becomes a source of excessive fatigue and discom- 
fort. Warmth is better attained by putting on several layers 
of light, loose-fitting garments, than fewer layers of hea\y 
clothing. As before stated, it is not the clothing itself, but 
the air imprisoned by it, which secures warmth ; and the air 
is not only held within the meshes of the cloth, but a stratum 
is retained underneath each additional layer of clothing. It 
is, therefore, desirable to multiply the number of layers, which 
is only possible when hght materials are used. 

463. It should be Loose. — Every one knows that loose 
clothing is warmer than that which fits the body closely, and 
this alone should be sufiicient reason for adopting it. But 
tight-fitting garments are in other respects very injurious. 
They obstruct the flow of blood, restrict the natural motions 
and healthy exercise of the parts, and not unfrequently pro- 
duce deformities of the worst character. Many have observed 
the ellects of a tight-fitting head-dress in obstructing the circu- 
lation. Constrictino* the neck is even worse. The ec^'eat veins 
which carry the blood from the head back to the heart lie very 
superficially in the neck, and, when any thing tight is worn 
closely about it, the flow of blood is obstructed, and venous 
congestion of the brain results. 

464. Compression of the Chest and Abdomen. — It is, 
likewise, of the greatest importance that the motions oi the 
chest and abdomen should not be interfered with. There is 
probably no part of the body where freedom of action and of 

15 



338 ELEMENTARY HYGIENE. 

circulation is more absolutely required tlian here. At the 
junction of the chest with the abdomen are located the lower 
portions of the lungs, the spleen, stomach, liver, etc. There 
are also given off from the aorta at this point several large ves- 
sels, which carry blood to the adjacent viscera. The diaphragm, 
the most important muscle engaged in the process of respiration, 
is likewise found in this immediate vicinity. Every function 
of the body calls for the utmost freedom of movement in this 
important region. And yet it is the almost universal practice 
among females to bind down these parts often to half their 
natural dimensions. Keference to Fig. 125 shows this to be one 
of the roomiest portions of the body when left in its natural 
condition. 



Fig. 125. 

A diagram showing the natural form of the healthy chest, and the proper poBition 
of the organs which it contains. 

Fig. 126 shows the distortion which often results from com- 
pression. This deformity is not the worst of the evils which 
follow the practice of compressing these parts. The diaphragm 
is hampered in its actions, and the process of respiration thus 



MANNER OF DRESSING THE BODY. 3d\) 

directly interfered with. The lungs and heart are compressed, 
and the stomach and liver either forced out of place, or, what 




Fig. 126. 
A diagram showing the deformity produced by compression. 

is worse, squeezed into much less space than they would natu- 
rally occupy. The portal circulation is thus obstructed, and 
the viscera, like the brain in the former case, become the seat 
of venous engorgement. 

It is hardly necessary to add that the troubles induced by 
this state of things are of the most serious character. Diseases 
of the liver, dyspepsia, and consumption are among its legiti- 
mate and certain results, while other disorders of a less detinite 
character are, no doubt, traceable to the same efficient cause. 
The compression, when early applied, as it usually is, tiiids the 
bones of the chest soft and yielding, so that they readily give 
way. If the constriction is continued, as it is likely to be, for 
fear of losing the " beauty of the form," the bones, as age ad- 
vances, harden and conform to the unyielding limitations with- 



340 ELEMEJSrrARY HYGIENE. 

out, and thus arise permanent and life-long deformity of the 
chest and continued restraint of its important organs. The 
persistence with which this practice is followed by females, 
betrays either outrageous ignorance or an almost criminal dis- 
regard of consequences. 

465. Compression of the Feet. — This is a common prac- 
tice, that often results in distortion and great discomfort. Fig. 
127 shows the deformity produced by compression, while Fig. 





Fig. 127. Fig. 128. 

128 gives the natural shape of the foot. "When we are walking 
with the feet unrestrained, each foot, as it receives the weight 
of the body, broadens slightly, and lengthens to the extent of 
half an inch or more. Freedom of motion in the foot itself is 
thus seen to be a natural requisite, and without it case, grace, 
and comfort in walking are out of the question. Compression 
by the boot or shoe not only prevents this freedom of action, 
but also gives rise to deformity of the feet. The sole of the 
boot should be as wide as and somewhat longer than the foot 
when the weight of the body is resting upon it. The upper- 
leather requires to be soft and yielding, and not so tight 
as to pinch the foot down upon the sole. The toe of the 
boot ought to be wide, leaving the toes perfect freedom of 
movement. If too narrow, they are made to override each 
other, thus producing ingrowing toe-nails, corns, bunions, etc. 
The heels should be low and broad, so as to furnish a firm 
support. High heels throw the feet forward toward the 



MANNEE OF DRESSESTa THE BODY. 341 

points of the boots, and tend to produce flattening of the arch 
of the foot. 

466. Clothing should favor TTniformity of Temperature. 
— In health, all parts of the body have an average temperature 
of about 98° Fahr., and this is regulated and maintained by 
the circulation of the blood. This uniformity of temperature 
throughout the body is of the utmost importance, and as it is 
controlled through the circulation, any thing which disturbs 
this should be carefully avoided. Clothing may do it in various 
ways, producing local results often of a very injurious nature. 
Compression obstructs the flow of blood, and at the same time 
forces out what the part already contains. Over-clothing par- 
ticular points leads to the accumulation of heat and consequent 
relaxation of the vessels, when more than the normal supply of 
blood flows in, and congestion results. A lack of clothing, by 
affording insufllcient protection, permits the rapid escape of 
heat, and thus the temperature may fall below the healthy 
standard, while the surface blood is driven inward, producing 
congestion of the internal organs. Compression, wherever ap- 
plied, causes paleness, diminishes the calibre of the vessels, and 
is attended with an immediate low^ering of the temperature. 
Hence the cold feet and hands caused by tight boots and tight 
gloves. Of the other causes of disturbance, both are generally 
operating: while one part is overheated by a superabundance 
of clothing, another part may at the same time be suffering 
from cold. This is often the case with children, who may be 
seen in cold weather loaded with clothing about the chest and 
neck, while the legs and lower portions of the trunk are hardly 
more than covered. 

467. Disturbance of Vascular Parts. — Certain organs of 
the body are more vascular than others; that is, their blood- 
vessels are larger and more numerous, and they receive a pro- 
portionately larger supply of blood. The throat, the lung?=, the 
liver, and kidneys, are examples. Owing to their extreme 
vascularity, these organs are peculiarly liable to become the 
seat of engorgement if overheated by clothing or otherwise, 



342 ELEMENTARY HYGIENE. 

especially when other regions are at the same time imperfectly 
protected. An instance forcibly illustrating the bad eflects of 
habitually overheating a part recently came within the writer's 
notice. A boy, 16 years old, had been daily employed for a 
period of about three months in the winter season, in a work- 
shop where he was obliged to stand with his back very near a 
hot stove. This maintained an almost constant congestion of 
the kidneys, which had led, when I saw him, to w^ell-marked 
Bright's disease. The region of the kidneys is commonly 
overdressed by the lapping at this point of the garments which 
clothe the trunk and lower extreniities. In this way, two or 
three extra thicknesses are commonly obtained, and a tendency 
is thus created toward the accumulation of blood in these im- 
portant organs. 

468. Overdressing the Throat. — Muffling the throat is 
very common, particularly among children, and it is often re- 
marked that those who wrap it the most are the ones who suf- 
fer most from its disorders. This practice is perhaps respon- 
sible for more sore throats, coughs, and croups, than all other 
causes put together ; and when this overdressing of the neck 
is supplemented, as it commonly is in children, by short dresses 
and thinly-clad extremities, the conditions are most complete 
for the production of all sorts of throat and lung affections. 

469. Flannel next the Skin. — Uniformity of temperature 
is greatly promoted by constantly wearing next the skin some 
non-conducting material, such as flannel or silk. This prevents 
sudden chilling of the surface, which, in our variable climate, 
is liable to take place at any time, unless specially guarded 
against. Flannel is found by experience to be best for this 
purpose ; but, in those cases where it irritates the skin, cotton- 
flannel or silk may be conveniently substituted. Linen should 
never be used. The good effects of wearing flannel next the 
skin the year round are unquestionable. In both cold and hot 
climates it is found to be an efficient safeguard against dis- 
ease ; and there are few who cannot soon become accustomed 
to its use. 



MANNER OF DEESSING THE BODY. 343 

470. Clothing of Children. — Erroneous notions upon this 
subject lead to wrong practice, which is followed by the most 
pernicious consequences. Many entertain the idea that their 
constitutions may be hardened by exposure ; but, instead of any 
such vague benefit, specific and positive injuries are produced. 
Clothing, diet, and healthy growth are intimately correlated. 
Food is the source of all bodily function and power, and the 
supply of force from this source is necessarily limited. Each 
day's bodily exercise, each day's mental exercise, each day's 
waste, repair, and growth of all the organs, and the definite 
amount of heat required to maintain the system at 98° during 
the 24 hours — each and all are at the expense of the food daily 
digested, and any overtaxing in one direction involves corre- 
sponding deficiencies in others. If the body is insufficiently 
clothed, there is extra loss of power through waste of heat, and 
a necessary reaction upon the constitution. The waste of heat 
entails a lowering of vital processes, and body and brain fail to 
reach a vigorous development. Thus, the naked legs and arms 
of children, which so please the vanity of silly mdfE^s, are at 
the cost of their perfected constitutions. The exuberawenergy 
of childhood is not to be carelessly squandered, but carefully 
economized and directed to its highest uses. 

471. Clothing in Advanced Age.~As the bodily func- 
tions decline in vigor with advancing life, the protecting influ- 
ence of clothing becomes more necessary. The incapability 
of the aged to resist cold is well known, and fatal consequences 
frequently follow from persisting in old habits, and neglecting 
the indications of Nature for increased warmth and abundance 
of apparel. 



344: ELEMENTARY HYGIENE. 

CHAPTER XIX. 

EXERCISE AND HEALTH. Q--:^ 

Section L — Labor and Exercise, 

472. Man intended for Action. — Anatomy and Physi- 
ology alike proclaim that the purpose of the human constitution 
is activity. The provision for varied and complex movement 
is seen in the jointed skeleton, the contractile muscles, the 
controlling nerves, and the power-supplying apparatus of di- 
gestion and circulation. Thus the whole economy of the 
organism testifies that its end is action. Moreover, the cir- 
cumstances of life involve the necessity of action. Eflfort must 
be put forth for the maintenance of existence, and for the 
gratification of the various faculties of our nature. 

473. Labor. — This great end of our being finds its legiti- 
mate ai^anmiral expression in lahor^ which is human action 
applied lb oYpious materials and objects, for the attainment of 
some productive or usefid result. The necessity of labor is thus 
doubly provided for in the construction of the human fabric 
and the order of external nature, and, when performed with 
due regard to the laws and rights of our being, it is in every 
respect a benefit and a blessing. But when* pursued to excess, 
as has unhappily been too common in the past history of man- 
kind, it is perverted into degrading drudgery, and then be- 
comes a curse. 

As skilful and effective labor involves intelligence, time 
and thought are needed to secure aptness in its performance, 
and the narrower the range of effort, the greater is the facility 
attained. This restricts the individual to specific pursuits, and 
gives rise to that diversified system of division of labor which 
has grown to such vast complexity in modern society. The 
tendency of this system is to call into intense exercise a portion ^ 
— ^perhaps but a small portion — of the activity of the individual, . 



LABOR AND EXERCISE^ 345 

and to leave tlie remainder of his powers unused. In many vo- 
cations tlie hands only are brought into requisition, while the 
body is unexercised ; in others, the muscular system alone is 
involved, while the brain remains unoccupied ; in other cases 
the brain is active and the body at rest, or perhaps a portion 
only of the brain is exerted, as in numerical computation and 
managing accounts, 

474. Exercise. — Thus the tendency of modern life is to 
overwork a narrow portion of the human constitution and un- 
derwork the remainder, so that a large part of it is not called 
into the activity for which it was designed, and which is neces- 
sary to health. There are few persons whose habitual activi- 
ties are so complete that they do not require to be supple- 
mented by various artificial exertions, while this need is still 
more imperative with those of sedentary habits and the classes 
of leisure. To meet these various emergencies, and give to 
the unused portions of the human system their requisite action, 
is the object of exercise. 




Section II. — Effects of Regulated Exemm, 

475. Transformation of Physiological Forces. — All those 
vital processes which are essential to life, as digestion, circula- 
tion, respiration, secretion, are carried on independently of the 
will, and give rise to a large and constant amount of activity in 
the system. But labor and exercise are performed by calling 
into action an additional system of agencies — those of the vol- 
untary muscles — and to maintain these in a state of activity, 
involves an extra requisition upon the various involuntary 
organs. As the materials of the body are derived from the 
substance of the food, so all vital power is derived from the 
force stored up in the food. Organic matter is in a state of 
molecular tension, and, when decomposed, these tensions are 
given out in the form of physical forces. Food is organic mat- 
ter, suited to undergo assimilation, and tlien to give out its 
molecular tensions in various forms, as animal heat, muscular 
15* 



346 ELEMENTAEY HYGIENE. 

power. It follows that in work, or exercise, the voluntary 
muscular system draws upon the involuntary functions for its 
supply of energy ; and hence, in proportion to the force ex- 
pended, is the general exaltation of the vital processes. 

476. Exercis3, Waste, and Repair. — Bodily exertion thus 
increases atomic changes, and quickens that metamorphosis of 
tissues in which health essentially consists. Exercise is at the 
expense of waste ; waste involves repair, and these augmented 
processes call into higher action the whole apparatus of supply 
and excretion. Habitual exercise is thus the cause and condi- 
tion of that vital renovation of parts which is the source and 
measure of constitutional vigor. 

477. Ejffect upon the Circulation. — As the circulation 
ministers immediately to all the functions, its energy rises and 
falls with their activity. Exercise increases the movements of 
the heart in both force and frequency, and accelerates the flow 
of blood through all parts of the body. The circulation is also 
aided by the contractions of the voluntary muscles, which, by 
pressing upon the walls of the veins, tend to force along the 
current of blood. Moreover, this increased activity of the cir- 
culation meets the increased demand of the muscles for new 
material, to renew the disintegrated structures ; and it also 
elFects the speedy removal of all waste products, by rapidly 
transferring them to the proper eliminating organs. Thus, the 
complex stream from which nutritive materials are constantly 
drawn, and into which waste matters are constantly poured, is 
directly affected, both in its composition and rate of movement, 
by the state of action of the voluntary muscles. 

Exercise also, it is well known, heightens the calorifying 
functions. It is through the increased activity of the circula- 
tion that the body is warmed by exercise. This is the reason 
why walking is so effectual in warming the feet, and why 
exertion of any kind raises the temperature of the parts em- 
ployed. 

478. Effect upon Respiration. — Circulation and respira- 
tion are accelerated together by exercise, as whatever quickens 



EFFECTS OF REGULATED EXERCISE. 347 

the pulse hastens the breathing. It being the office of respira- 
tion to furnish the prime mover of vital changes — oxygen — 
and to rid the system of the chief product of such change — 
carbonic acid — this process is doubly subservient to the great 
dynamic objects of the organism. It follows that a fundamen- 
tal condition of exercise is unimpeded respiration. If the pul- 
monary circulation and the elimination of carbon are in any 
way interfered with, the power of continued exertion rapidly 
declines. As thus muscular movement depends immediately 
upon the excretion of carbonic acid from the system, and as 
this, in turn, depends upon the state of the air itself, we see 
that an impure atmosphere is unfavorable to vigorous and 
healthful exercise. This explains the lassitude and indisposi- 
tion to eifort in unventilated houses, workshops, and factories. 
Exercise should, therefore, as much as possible, be carried on 
in the open air, or in places which admit of the freest ven- 
tilation, 

479. Effects upon Digestion. — As power comes from food 
in the case of the living machine, increased expenditure of 
power, of course, implies increased consumption of food; hence, 
exercise sharpens the appetite. In those who indulge in active 
and regular exercise, digestion is effected wath greater ease, and 
the process is more rapidly and more thoroughly completed 
than in those of inactive habits. In many cases, where the 
digestive function has become impaired, either from habitual 
inactivity or a too close application of the mind, relief can 
easily come through systematic and judicious exercise. Im- 
mediate exertion after a full meal is injurious, for several rea- 
sons. The distended condition of the stomach interferes with 
the free movement of the diaphragm and heart, and tluis both 
respiration and circulation are mechanically impeded, while 
the diversion of blood and nervous force to the muscles with- 
draws them from the digestive organs and hinders their 
functions. 

480. Effect upon the Skin. — With exercise, the skin be- 
comes redder and hotter, from the increased amount of blood 



348 ELEMENTARY HYGIENE. 

it receives. During exertion, heat is rapidly developed within 
the body, but its accumulation is prevented by the escape of 
water through the skin. No amount of external cold is able to 
prevent this outward passage of fluid, though it may slightly 
hinder evaporation. There is, therefore, little danger of chill 
during active exercise ; but when exertion is over, there is great 
danger of it, for the heat of the body rapidly declines, while 
evaporation continues, which still more reduces the tempe- 
rature. During exertion, the skin may be exposed without 
danger; but during the intervals of rest, it should be covered 
sufficiently to prevent the least feeling of coolness of the 
surface. 

481. Exercise should be Regular. — Like eating and 
sleeping, exercise should become a regular and persistent daily 
habit. It is an imperative necessity of the system, and, as an 
element of personal hygiene, is indispensable. If it be resorted 
to in any form of bodily training, as in military drill, rowing, 
or other athletic effort, it is found that the periods of exertion 
must not be less than half an hour, in order to take hold of the 
system, and produce the positive effect of bodily discipline. 

482. The Mind in Exercise. — Exercise, or simple muscu- 
lar movement, whatever may be its value for health, has in 
itself very few attractions, and will be avoided rather than prac- 
tised, unless there is connected with it something capable of 
calling the mind into pleasurable activity. When taken merely 
from a sense of duty, or '' because the health requires it," ex- 
ercise becomes a drag and a bore, without vigor and of little 
benefit. When, however, it can be made the means of enjoy- 
ment, by associating with it something agreeable and exhila-' 
rating, it becomes at once spontaneous, vigorous, and hearty, 
and its value to the health, both of mind and body, is increased 
in a great degree. 



EXCESSIVE AND mSUFFICIENT EXERCISE. 349 



Section III. — Excessive and Insufficient Exercise. 

433. Effects of Over-exertion. — With the proper amount 
of exercise, the muscles increase in size, hardness, and elastic 
vigor, until the equilibrium of waste and repair is carried to its 
highest point. Exercise is at the expense of the part in action ; 
in vigorous exertion, decomposition prevails over renewal. The 
muscles can bear this for a certain length of time, and then de- 
mand rest, in which repair prevails over waste, and restores the 
balance. If exertion be pushed still further, the equilibrium is 
lost; destructive changes prevail over reparative, and the mus- 
cle begins to degenerate and lose power. Prolonged exertion, 
without sufficient rest, impairs nutrition, and renders the mus- 
cular fibres soft and flabby. Nature thus provides for the 
rhythm of activity and repose. The involuntary muscles, as we 
have seen, — those of the heart and chest,— act in this inter- 
mitting way, and are thus kept up to a constant state of vigor. 
The law is equally imperative for the voluntary muscles, and 
the proper rest is to be secured either by ceasing from activity, 
or by calling different sets of muscles into alternate exercise. 

When the muscles are weak, repair goes on more slowly 
than when they are "in condition." Hence, in any effort at ac- 
quiring strength by exercise, either after sickness or prolono-ed 
sedentary occupation, the exercise should at first be very lii^ht, 
and of short duration, with long intervals of rest. As the 
strength slowly increases, the exercise may be increased, but 
exhaustion in all such cases is to be carefully avoided. 

Excessive exercise often produces palpitation, and some- 
times hypertrophy and valvular disease of the heart. During 
exertion, if the heart is not oppressed, its movements, though 
rapid and forcible, are regular and equal ; but when it becomes 
embarrassed, the pulse-beats are quick, unequal, and at last be- 
come irregular, indicating injury to the organ. All great or 
sudden efforts ought to be carefully avoided, as tliov not onlv 
affect injuriously the muscular system, by direct overstrain, but 



350 ELEMENTARY HYGIENE. 

it is at such times that blood-vessels are ruptured, and that the 
walls of important cavities give way. 

Eest after exertion is one of the most important conditions 
of health. Work or exercise carried habitually to the length 
of exhaustion, by lowering the bodily vigor and depressing the 
powers of the constitution, not only diminishes resistance to 
the encroachments of disease, but greatly reduces the capability 
of recovery in cases of sickness. Particularly in childhood, 
when the bones are yet incompletely ossified, and the muscles 
undeveloped, excessive labor or exertion is liable to entail per- 
manent injury. If persisted in, arrested development of either 
body or mind can hardly fail to result. From the age of 15 
to 25, although full growth may have been reached, the powers 
of endurance have not attained their maximum, and all ex- 
hausting tasks require to be avoided. Young soldiers break 
down under the toils and privations of the camp sooner than 
mature men. This is also true in civil life, where the young 
and immature are called upon to match their powers with 
those in the maturity of manhood ; and the remark is equally 
applicable to the female, under the spur of competition with 
the male sex. The consequences are seen in broken-down 
constitutions and premature decay. 

484. Efifects of Insufficient Exercise. — Inaction contra- 
venes the supreme design of the human constitution, and is 
therefore adverse to its health. As bodily vigor results only 
from active and well-regulated exercise, the absence of such 
exercise must entail bodily debility. As exertion favors nutri- 
tion and the healthy development of active parts, inaction im- 
pairs nutrition, reduces the size of the muscles, and gives rise to 
feebleness. The amount of injury in the case may, however, 
depend much upon accompanying circumstances. If abstinence 
from exercise be attended by abstinence in diet, there will still 
be loss of power, low vitality, and diminished resistance to 
morbific influences ; the evils will be rather of a negative char- 
acter. But if deficient exercise be accompanied by a free in- 
dulgence of the appetite, perverted nutrition and positive dis- 



EXCESSIVE AND mSUFFICIENT EXERCISE. 351 

ease will be the necessary consequence. Nutritive materials 
that would be reduced and excreted through bodily exertion, 
accumulate in the system, clogging its movements, deranging 
its functions, and deteriorating its structures. Not only is 
there an abnormal accumulation of fat, amounting to actual 
disease, but an aberration of the nutritive forces, that under- 
mines the healthy structure of the tissues. Nor is this muscu- 
lar deterioration limited merely to the parts that are unused ; 
the involuntary mechanism becomes implicated. Deficiency 
of exercise often leads to fatty degeneration of the heart, with 
loss of power and derangement of the circulation. In short, 
as vigorous and systematic exercise is a prime condition of the 
general health, so the want of it favors the approach of disease, 
which may take many forms, according to the circumstances 
of the constitution. 

485. Amount and Conditions of Exercise. — As to the 
amount of exercise necessary to meet the requirements of the 
healthy individual, no precise rules can be given ; that amount 
will vary with many circumstances. Persons of sedentary 
habits would be seriously injured by attempting to perform 
an amount of work which, to others of a more active turn, 
would hardly exceed the bounds of recreation. The inmate 
of the workshop or factory would be speedily exhausted by 
the ordinary tasks of the out-door laborer. In any given case, 
the amount of exercise should be determined and regulated by 
the state of the constitution. That exercise is deficient which 
does not engage the vigorous action of the chief muscles of the 
system for a considerable period each day ; and that too groat 
which, passing beyond the point of simple fatigue, is prolonged 
to the period of exhaustion. 

The sedentary, if they would acquire strength, must begin 
with light exertion, limited to short periods, and take ample 
time for rest. Nothing is more erroneous, and, if carried into 
practice, more injurious, than the notion that great exei*tion 
will augment the strength of those unaccustomed to active ex- 
ercise. The growth of muscle, in both substance and poAvor, 



352 ELEMENTARY HYGIENE. 

is a gradual process, and one that is retarded ratlier than has- 
tened by overwork. If exhaustion or restlessness follows ex- 
ercise, we may be certain that it has been overdone, and will 
he productive of weakness rather than strength. 

As has been stated in a previous chapter, an abundant sup- 
ply of pure air is at all times a vital necessity of health ; but 
the demands of the system in this respect are greatly increased 
during active muscular exertion. As the diminution of waste 
products is a result of oxidation, it is hindered by breathing 
an impure atmosphere. For this further reason, open-air exer- 
cise is much superior, as a health-promoting agent, to that 
carried on within the walls of a gymnasium or other confined 
area. 

486. Remedial Influence of Exercise. — If thus exercise be 
an essential condition of health, and the want of it a fmitful 
cause of disease, it is obvious that only hy the reestablishment 
of the needed exercise can health be regained. But in many 
cases the diseases induced make the required effort either im- 
possible or very difficult. What is known as the movement- 
cure is a kind of dynamic treatment, in which the patient is 
subjected by the physician to various kinds of artificial exer- 
cise. In many cases of local weakness and partial paralysis, 
by the help of skilfully-constructed mechanical contrivances, 
these parts are gradually brought into action, and healthy 
power slowly recovered. The principle in this case is valu- 
able, and, important as a remedial agency, its employment has 
accomplished much good, and more is to be expected from its 
fiirther development. 



RELATIONS OF MIND AND BODY. 353 

CHAPTER XX. 

MENTAL HYGIENE. 

Section I. — Relations of Mind and Body. 

487. Mental Health a Physiological Question. — Thus far 
we have confined attention mainly to the influences which act 
on the general bodily health, but the principles of hygiene 
have a still higher application. The mind has its states of 
health and vigor, of debility and disease, like the body, and 
these states are influenced by definite causes in the former case 
as well as in the latter. Mental philosophy, as commonly un- 
derstood, explains to us the operations of thought and feeling 
as we discover them in the working of our own minds, and 
takes little account of the part played by the corporeal system 
in the control of these processes. But if we would understand 
the conditions of mental health, and the nature and causes of 
mental impairment, the body must at once be taken into ac- 
count. The study of mental phenomena in their corporeal 
relations thus becomes the business of the physiologist. He 
sees that mind is not only intimately dependent upon the body, 
but that they have close and powerful reactions ; states of body 
determining conditions of mind, and states of mind influencing 
conditions of body. Nature presents the problem, not of mind 
separate, but of mind and body bound up in a living unity, and 
the physiologist must take the question as he finds it. 

488. The Brain and the Mind. — It is now universally 
admitted that the brain is the grand nervous centre of thought 
and feeling — the material instrument of the mind, and that all 
mental actions arc accompanied and conditioneJ by physiolo- 
gical actions. From the high complexity of composition of 
nervous matter, it is extremely unstable and prone to change. 
The brain is therefore not only, like all other parts of the body, 



351 ELEMENTARY HYGIENE. 

subject to the double metamorphosis of waste and repair, but 
the transformations take place in this organ with more rapidity 
than in any other part of the system. Upon these changes 
the mental operations are vitally dependent, and if in any way 
they are interfered with, there is disturbance of the intellectual 
processes. If the cerebral circulation is lowered, mental activity 
is diminished ; if accelerated, the mind's action is exalted. 
Various foreign substances introduced into the blood-stream 
alter the course of thought, some affecting it one way and 
some another, but each, through its specific physiological 
effects, producing characteristic psychological effects. Inflam- 
mation of the brain induces delirium, while different diseases 
of the organ, or perversions of the blopd circulating through it, 
give rise to various forms of insanity. 

It is important to note, not only that mind and body are 
both governed by laws, but that they are to a great extent 
governed by the same laws. Whatever improves the physical 
qualities of the brain, improves also the mind; whatever 
deteriorates the brain, impairs the mind. They have a com- 
mon development, are equally increased in vigor, capacity, and 
power by systematic and judicious exercise, and are alike in- 
jured by deficient or excessive efibrt. The brain is exhausted 
by thinking as much as the muscles by acting, and, like the 
exhausted muscles, it requires time for the restoration of vigor 
through nutritive repair. As thus the mind is dependent upon 
the conditions of the brain, while the brain is controlled by 
the bodily system, we see how impossible it is to deal with 
the mental powers in a practical way without taking the ma- 
terial organization into account. 

The objection often made, that this method of considering 
mind involves or leads to materialism, is altogether groundless. 
Materialism is a doctrine of causation which affirms that mind 
is a product of organization. But the degree to which mind is 
organically conditioned and limited is a pure question of fact 
and observation, and is totally independent of all speculation 
upon the former subject. If, to assert that " the brain is the 



RELATIONS OF MIND AND BODY. 355 

organ of the mind," involves materialism, it can only be said that 
all intelligent persons are to be ranked as materialists; but if 
not, then certainly the physiological inquiry which aims merely 
to trace out the details of the connection between mental mani- 
festations and corporeal states, is not obnoxious to the charge. 
There is nothing in the subsequent working out of the particu- 
lars that is not involved in the first broad assumption. 

489. Mental Health and Disease. — The observations made 
in regard to the true nature of diseases (361-2) — that they are 
nothing more than perverted physiological actions — need to be 
here repeated with emphasis. Those who habitually think of 
the mind as a separate entity merely coexisting in some vague 
way with the body, will naturally look upon mental derange- 
ments as disorders of this entity — diseases of an abstraction. 
But this view has proved misleading and injurious in the 
extreme. So long as maladies of the mind were regarded as 
demoniac possessions, or as " fermentations taking place in a 
spiritual essence," all rational causality was excluded, and the 
arts of relief and prevention were impossible. When, how- 
ever, it became established that mind depends upon definite 
physiological conditions, there was no escape from the conclu- 
sion that physiological perversions are causes of mental 
derangement. " Fair weather and foul equally depend upon the 
laws of meteorology ; health and disease equally depend upon 
the laws of animal life." As mental health is dependent upon 
the due nutrition, stimulation, and repose of the brain, mental 
disease is to be regarded as resulting from the interruption or 
disturbance of those conditions. 

In showing that mental weakness is a concomitant of bodily 
debility, and mental aberration a consequence of bodily dis- 
order, the physiologist lays the sure foundations of a practical 
Mental Hygiene^ the province of which is to consider the various 
causes which disturb the harmony and impair the vigor of 
mental actions. Taking note of the multiplied forms and de- 
grees of disturbance and degeneracy to which the mental na- 
ture of man is subject, it traces them to their numerous causes, 



356 ELEMENTARY HYGIENE. 

and discloses the extent to which they are avoidable. As bodily 
and mental health depend to a great degree upon the same 
conditions, all that has been said in the foregoing chapters 
concerning the sanitary influences which affect the corporeal 
system has likewise its bearing upon health of mind. But the 
mental aspects of the subject are so generally overlooked as to 
demand special consideration. 

Diseases of the brain are, above all others, complex and 
obscure. Those of subordinate parts affect only the organic 
functions ; but when the higher nervous centres become dis- 
ordered, thought, feeling, will, conduct, and character are im- 
plicated, and the whole circle of individual relations and actions 
becomes a study of symptoms — a field of diagnosis. So great 
is the difficulty and responsibility of the task, that only the 
educated and capable physician who devotes his life to this 
specialty is competent to deal with these cases. And yet all 
members of the community have a vital interest in the subject : 
because, first, health and vigor of mind are of the highest im- 
portance, while each person has these interests ia his own im- 
mediate care ; second^ the causes which undermine them are 
numerous and insidious ; third, every one is liable to be called 
upon to act responsibly with reference to others who may be 
the subjects of mental impairment ; fourth, society has a duty 
to perform toward the defective-minded, which should be per- 
formed, not ignorantly, but intelligently ; and, finally, because 
a real knowledge of the characteristics and causes of mental 
deterioration is the key to a true understanding of the consti- 
tution of human nature. 

While, therefore, that detailed and deeper understanding 
of these questions which is necessary to discriminate their 
minor distinctions is only to be expected of the professional 
expert, such a general acquaintance with the leading types of 
mental disease as will facilitate an under^anding of causes is 
needed for all. A section of the present chapter may there- 
fore be properly devoted to their description and illustra- 
tion. 



FOEMS OF MENTAL IMPAIEMENT. 357 



Section II. — Forms of Mental Impairment, 

490. Modes of Mental Action. — Mental effects are mani- 
fested by the brain in a threefold form, as Intellect^ Feeling^ 
and Will, The intellect is the perceiving or knowing part of 
the mind, including perception, memory, reason, imagination, 
and judgment. The meutal nature has also an affective side, 
consisting of feelings, sentiments, emotions, passions. The 
intellect is discriminative, and has relation to the reality or 
truth of things ; the feelings are impulsive, and have regard to 
pleasure or pain. The will is the determinative or volitional 
part of the mental constitution, and has relation to effect or 
action. The intellect is an eye that sees an end to be attained 
and the means of reaching it ; the feelings, or desires, furnish 
the impulse to its attainment, and when these rise to sufficient 
intensity, they issue in a volition, which puts the body in 
tnovement to secure the thing desired. 

These are not separate elements of our psychical being, but 
inter work so closely and harmoniously as to give rise to per- 
fect mental unity. Still the distinction is so fundamental as 
to be recognized, both in the study of the healthy human fac- 
ulties and also in their morbid manifestations. There is an 
insanity which is predominantly intellectual, disclosing itself in 
disordered sensation, perception, memory, judgment, and 
reason, without deeply involving the feelings ; and there is an 
emotional insanity, which consists in the unregulated action of 
the impulses, while the intellect may be but slightly disturbed. 
But usually all these faculties are more or less involved in the 
mental disturbance. 

491. Aberrations of the Intellect.— In Chapter XL, Sec- 
tion XL, itNvas stated that, owdng to certain conditions of body, 
fiilse appearances and various disturbances of the senses are 
liable to arise. These errors are of several kinds. 

Hallucinations, — The case of Mrs. A., the details of which 
were given (296), belongs to a class of deceptions in which 



358 ELEMENTARY HYGIENE. 

objects appear to be present, when in reality they are not ; 
sensations are perceived, although there are no material objects 
to produce them. All the senses are subject to these decep- 
tions; sights, sounds, tastes, smells, and contacts are experi- 
enced when there are no realities to cause them. Mental mis- 
takes of this kind are known as hallucinations. 

They are very common, and the greatest minds are often 
subject to them. Byron fancied he was visited by a spectre, 
which, he confesses, was but the eftect of an overworked brain. 
Dr. Johnson said that he distinctly heard the voice of his 
mother calling '' Sam," although she was, at the time, residing 
a long way oft'. Goethe positively asserts that he one day saw 
the exact counterpart of himself coming toward him. Descar- 
tes, after long confinement, was followed by an invisible per- 
son, calling upon him to pursue the search of truth. Luther 
imagined he saw the devil, and threw his inkstand at him. 
HuUucinations may thus coexist with a sound state of the rea- 
son, which recognizes their true character. In the insane they 
assume a thousand singular and fantastic forms. 

Illusions, — Again, an object may be perceived, but misun- 
derstood, or mistaken for something else. In this case there 
is an illusion. These, also, are very common. The apparent 
flight of the trees and fences as we glide swiftly along in the 
railway-train is an example of illusion, which is immediately 
corrected by the judgment. The mirage at sea, or on the des- 
ert, is another illustration. When the imagination becomes 
morbidly excited through the influence of fear, superstition, or 
otherwise, there is great liability to illusion. The folds of 
drapery, or pieces of furniture, seen by a pale, uncertain light, 
are taken for apparitions; the clouds are transformed into 
fighting armies, or the heavens appear filled with blood. "When 
the mind becomes more deeply perverted, one person is mis- 
taken for another ; animals are mistaken for men, and con- 
versely, an old hat for a royal crown, and a handful of pebbles 
for heaps of gold. 

D elusions. ^^In the foregoing cases the seat of error is, not 



FOEMS OF MENTAL IMPAIEMENT, 359 

the senses themselves, but the judgment in relation to objects 
of sense. But the mind is liable to deceptions, and various 
false notions, which have no immediate reference to sense-per- 
ceptions, as where a person believes he is a prophet, or a king, 
or is the victim of a conspiracy to take his life, or has lost his 
soul. False impressions of this kind are characterized as delu- 
sions. 

From the illustrations given, it will be seen that hallucina- 
tion and illusion may coexist with a sound state of the reason, 
which comprehends their real nature, and it is maintained that, 
in some cases, the mind can rectify its own delusions. But if, 
in any of these circumstances, the individual is incapable of 
reaognizing or correcting them when an appeal is made to his 
reason, the case is one of delusional insanity, or insanity of the 
intellect. 

These delusions are, of course, liable to involve the feelings, 
and the character of the insanity may depend upon the emo- 
tions excited. A person under the delusion of pride, who 
fancies himself an emperor or an angel, may be harmless ; but 
if, under the delusion of fear, he imagines those around him to 
be enemies, seeking to take his life, or if he hears voices com- 
manding him to kill them, his insanity is dangerous, and ne- 
cessitates restraint. 

492. Emotional Insanity. — By this is understood a de- 
rangement of the affections, an abnormal deficiency of moral 
sense, or morbid activity of the propensities, which gives rise 
to extravagance of conduct. These diseases of feeling do not 
necessarily involve insanity of the intellect. A persoii may 
have a good degree of intelligence with a very low and defec 
tive moral nature, or he may be driven by insane impulses to 
the commission of acts which his judgment condemns. In the 
healthy balance of the faculties, reason guides the passions ; 
but these may be so morbidly exalted, that reason loses its 
empire ; it can counsel, but no longer control. Moral perver- 
sities of character may be congenital, or from birth, when the 
whole life of the individual is morally unhealthy, or it may be 



360 ELEMENTARY HYGIENE. 

due to various causes, the effects of wbich are seen in a pro- 
found change in the conduct. 

Examples of the former kind are numerous where inertness 
or obtuseness of the moral nature, and a controlling activity 
of the lower propensities, have been witnessed from childhood, 
and over which threats, rewards, and punishments were with- 
out influence. Cases of this land are w^ell represented by the 
individual described by Dr. Crawford : 

*' He exhibited a total want of moral feeling and principle, 
yet possessed considerable intelligence, ingenuity, and plausi- 
bility. He has never been different from what he now is ; he 
has never evinced the slightest mental incoherence on any 
point, nor any kind of hallucination. He appears, however, so 
totally callous with regard to every moral principle and feeling, 
so totally unconscious of ever having done any thing wrong, so 
completely destitute of all shame or remorse when reproached 
for his vices or his crimes, and has proved himself so utterly 
incorrigible through life, that it is almost certain that any jury 
before which he might be brought, would satisfy their doubts 
by returning him insane." ^ 

In the other class of cases, persons in whom mental de- 
rangement had never appeared, become the subjects of a 
gradual change of feeling and conduct. They are noticed 
to be * unusually absorbed, reserved, and irritable upon the 
slightest provocation. As the cloud gathers, there is increas- 
ing suspicion and moroseness, and, without perhaps knowing 
the reason, the patient's friends regard him as an altered man. 
At last the storm bursts, and some outrageous act is committed. 
If it is not a breach of law, he is pronounced insane, and sent to 
the asylum ; if in violation of law, he is probably declared a 
criminal, and sent to prison or to execution. Or the case may 
terminate in suicide, under a blind impulse to self-destruction. 

A good illustration of emotional insanity is given by Dr. 
Maudsley. A married lady, aged thirty-one, who had only 
one child a few months old, was for months afflicted with a 
strong and persistent suicidal impulse, without any delusion. 



FORMS OF MENTAL IMPAIRMENT. 361 

or any disorder of tlie intellect. After some weeks of anxious 
care from her relatives she was sent to an asylum, so frequent 
were her suicidal attempts. She was quite rational, even in 
her great horror and reprobation of the morbid propensity, and 
bitterly deplored the grief and trouble she caused her friends. 
Nevertheless, her attempts at suicide were unceasing — at one 
time trying to strangle herself, and again refusing all food. 
After she had been in the asylum for four months she appeared 
to be undergoing a slow and steady improvement, and watch- 
fulness was somewhat relaxed ; but one night she suddenly 
slipped out of a door, climbed a high garden-wall with sur- 
prising agility, and threw herself headlong into a reservoir of 
water. She was got out before life was quite extinct ; and 
after this attempt, gradually regained her cheerfulness and love 
of life. Her family was saturated with insanity. Dr. Maudsley 
exclaims : " In face of such an example of uncontrollable im- 
pulse what a cruel mockery it is to measure the lunatic's respon- 
sibility by his knowledge of right and wrong ! — implying that 
there are those who would limit insanity to derangement of the 
intellect — a derangement so profound as to obliterate the capa- 
bility of even discriminating between right and wrong. There 
has been a reluctance to admit the existence of what is termed 
moral insanity on the part of many, who confine their attention 
to the practical difficulties it involves as regards society ; but 
with those who make it their business to study the facts in a 
true scientific spirit there is no shadow of doubt in the matter. 
Examples, like those above mentioned, innumerable and end- 
lessly varied, but all presenting the same marked and essen- 
tial features, are to be rationally accounted for. It being ad- 
mitted that derangement of the intellect is due to disease of its 
organ, and furthermore that the brain is the instrument of 
feeling as well as of thought, there can be no escape from the 
conclusion that cerebral disorder may also give rise to insanity 
of the feelings and propensities. The conviction of all emi- 
nent physiologists and pathologists upon the subject is thus 
expressed by Dr. Carpenter : 
16 



362 ELEMENTARY HYGIENE. 

"^ There may be no primary disorder of the intellectual 
faculties, and the insanity may essentially consist in a tendency 
to disordered emotional excitement, ^vhich affects the course 
of thought, and consequently of action, without disordering 
the reasoning powers in any other way than by supplying 
wrong materials to them. Moral insanity may, and frequently 
does, exist without any disorder of the intellectual powers, or 
any delusion whatever.' " 

Dr. Eay makes the following judicious and forcible obser- 
vations upon the practical aspects of this subject: "While 
people clearly recognize the infinite diversity of intellectual 
gifts, and would no more expect the fruits of genius and talent 
from those who had been denied by Nature the sHghtest por- 
tion of either, than we should grapes from thorns or figs from 
thistles, they arc in the habit of believing that for all practical 
purposes the moral endowments of men are equal. Not exactly 
that they are equally benevolent, equally honest, equally true to 
the right and the good ; but that they might be if they chose. 
They never would think of saying to men, ' Here is poetry, 
here is philosophy, here is art ; you have the capacity to excel 
in either; take your choice, and be rewarded or punished 
accordingly.' 

" In the moral sense or faculty it is easy to recognize two 
difierent elements, viz., the power to discern the distinction 
between right and wrong, virtue and vice, the honest and the 
base, and the disposition to pursue the one and avoid the 
other. These elements, like those of the intellect, are une- 
qually developed in different men, which inequality may be 
either congenital or produced in after-life by moral or physical 
causes. And thus, though a person may act with perfect free- 
dom of will, unconscious of any irresistible bias, yet it is obvi- 
ous that his conduct is actually governed more by these varia- 
ble conditions of his moral nature than by any abstract notions 
formed by the intellect. 

" From the unquestioned fact that the brain is the material 
instniment of the mind, we are led to the inevitable conclusion 



FORMS OF MENTAL IMPAIRMENT. 363 

that its physical cocdition must modify more or less its mental 
manifestations, moral as well as intellectual. It is said, in 
the common form of speech, that a person is good or bad 
because he chooses to be the one or the other; and it is 
all very true, and sufficient perhaps, for our rough estimates of 
responsibility, but it does not answer the essential question, 
What determines the choice ? In the considerations here pre- 
sented, and in these only, is to be found a satisfactory answer 
to this question." 

493. Mania.— This is the term applied to a large class of 
cerebral disorders, in which the balance of the mental forces is 
lost, and the mind is in a state of preternatural excitement. It 
generally involves both the intellect and the feeling, but is 
more markedly a perversion of the impulses and propensities. 
Mania is either acute or chronic. 

Acute Mania is that form of mental disease commonly 
known as raving madness. It presents the aspect of high emo- 
tional excitement, the facial expression showing wildness, dis- 
traction, anger, or fear. In the paroxysms of acute mania, 
there is violence of speech and action. The patient raves, 
laughs, weeps, sings, laments, shouts, prays, and threatens ; his 
utterance is loud, rapid, and impetuous ; his voice harsh ; he 
manifests a total disregard of cleanliness and decency, and a 
dangerous destructiveness in relation to those around him, or 
even to senseless objects. 

"The condition of the mental faculties in acute mania pre- 
sents the widest differences. In many instances no trace of 
delusion can be discovered in a patient who is vociferating, 
swearing, laughing, reproaching, in constant movement, and 
without sleep. The observations and the remarks are some- 
times found to have a certain kind of cleverness, and shrewd 
appreciation of all that is taking place. The attention skips 
from object to object with choreic rapidity and abruptness, 
causing exaggerated and absurd emotional states, but in many 
instances not folsifying the judgment. In most cases, how- 
ever, delusions and hallucinations exist, and the task of detect- 



364 



ELEMENTARY HYGIENE. 



ing them is not difficult ; for in tins form of disease the patient 
is so demonstrable, that he usually dins his delusion into your 
ears '' (Bucknill and Tuke). 



Fig. 129. 




ACUTE MANIA. 

Eepresents tlie physiognomy of a case of acute mania. The patient is a woman thirty 
years of age, whose insanity was brought on by loss of character, want, and dis- 
tress. There is much emotional and intellectual disturbance, with compara- 
tively little derangement of the physical health. She believes that she is tormented 
by witches, and that she is compelled by them to make noises resembling dogs, 
cats, etc. She som.etimes destroys crockery and glass, and attempts to get up 
the chimney ; says she is cat to pieces, and that all the people around her are 
murderers. She strikes without warning straightforward blows at the faces of 
those who converse with her.* 

Chronic Mania is in most instances the result of the acute 
form of the disease. ^* It represents the rudderless and shat- 
tered state of the vessel after the tornado of raving madness 
has swept by." There is mental debility, persistent delusion, 
and less violent emotional disturbance. Chronic mania which 
has not passed through the acute stage frequently presents a 
remarkable vigor of the intellectual functions, in so far as they 
are not affected by delusion. 

Patients with this form of disease not only retain the per- 

* This likeness and those that follow (excepting the case of idiocy), which repre- 
sent the leading types of mental disease, are engraved from photographs taken from 
the life, and given in the authoritative work of Drs. Bucknill and Take on insanity. 



FOEMS OF MENTAL IMPAIRMENT. 



565 



ceptive faculties in all their activity, but the memory also is 
found to be tenacious, and even the judgment, on matters un- 
connected with the delusive opinions and perverted emotions 
peculiar to the case, may be found to be sufBciently trust- 
worthy. 

494. Monomania. — By this is understood a malady of the 
mind similar in character to mania, but limited to a single sub- 
ject, or involving only a single faculty. The patient may be 
the subject of a single delusion, which, being the result of dis- 
ease, he cannot overcome, although upon all other subjects the 
mind is healthy ; or some one emotion may acquire a morbid 

Fig. 130. 




MONOMANIA. 

Eeprescnts a case of the monomania of pride. It is the portrait of a woman of thirty- 
eii^ht, who hibors uiulor the delusion that she is her mnjosty's person; she is 
not her majesty, but her person, a distinction on which she lays great stress. 
She is proud and difirnified in her demeanor. Out of the commonest materials 
of dress she contrives to make a distinprnished ai)pearanee. She fastens the skirt 
of her dress low, so as to form a sort of train, and witli arms folded, the head, 
with its coronal ornaments, thrown i)roudly back, she would, if permitted, main- 
tain an erect and repil position from moviiinij: till niiiht. The inten!?e pride ex- 
pressed in the turn of head and eye, and in the lirm, compressed lips, cannot be 
mistaken. It is the physiognom'y of an exaggerated emotion transmuted into 
one dehisivc idea. 

ascendency and domination over the whole charaetov. Mono- 
manias are of various kinds. In Iioniicidal mimia there is an 
insane propensity to kill ; in suicidal mania an irresistible im- 



366 ELEMENTARY HYGIENE. 

pulse to self-destruction — a marked case of this kind has been 
already described (492) ; kleptomania is a diseased propen- 
sity to theft ; and in 'pyromania. there is an impulse to burn 
buildings. There are also monomanias of pride, vanity, etc. 
Dr. Bucknill describes the following representative case : ^^ An 
industrious, honest, well-informed artisan had a fever, w^hich 
resulted in an attack of maniacal excitement. From this he 
appeared to recover, but his temper was altered ; he became 
irritable, suspicious, aud quarrelsome. After the lapse of more 
than a year he declared himself to be the Son of God. His 
temper now improved, and at the present time the delusive 
opinion is, perhaps, as nearly the sole mental affection as is 
ever seen in cases of so-called monomania. Occasionally there 
are outbursts of violence toward those whom he thinks ought 
to obey him ; but on the w^hole he is docile, and on other 
matters reasonable, and works industriously at his trade." 

495. Melancholia. — The forms of mental impainnent thus 
far noticed are marked by undue intensity or exaltation of the 
cerebral function : we now pass to the consideration of those 
of an opposite character, which exemplify deficient or depressed 
conditions of the mental constitution. "While, for example, the 
monomaniac is excited, lively, and gay, *' living without himself 
and diffusing among others the excess of his emotions," the 
melancholiac is sad and sorrowful, and fastens all his gloomy 
thoughts upon himself. 

In simple melancholia the patient loses his interest in life, 
feels depressed and unequal to his duties, is cheerless, moody, 
and taciturn. His thoughts are centred upon his own desper- 
ate condition, wdiich he believes to be more wTctched than that 
of any other person. He magnifies every circumstance which 
can be regarded as of unfavorable omen, and is unable to realize 
those which are favorable ; he misconstrues every observation 
that is addressed to him, and when he reads, every sentence 
appears intended especially for him, if of a gloomy nature. 
One pours forth his grief in sad and w\ailing accents ; another 
is depressed and silent. He is a prey to gloomy apprehensions. 



FORMS OF MENTAL IMPAIRMENT. 



567 



forbodes constant evil, and often sits from morning till night 
bemoaning his unhappy situation. 

Melancholia takes a variety of forms. It may be an exag- 
geration of the patient's natural character, and have a long 
period of development ; it is often a consequence of other forms 
of insanity, and may spring from the grief that follows sudden 
calamity. Dr. Connolly records the case of a lady whose only 
son dropped dead in the midst of apparent health. The shock 

Fig. 131. 




MELANCHOLIA. 

Represents a case of suicidal melancholia. It is that of a carpenter of steady habits, 
agred fifty-six, and insane four months before admission to the asylum. He had been 
dull and depressed, and could not attend to liis trade ; refused to take food be- 
cause it was too good for him ; was restless by ^ay end sleepless by night ; said 
tliat he must be burnt or scalded to death, and made frequent attera'pts to get at 
the hot-water taps that he might scald himself, and to a duck-pond that he might 
drown himself. He said that his wife had given him poison in a cake, and after 
that he had to be fed with a spoon till the time of his di-ath, which occurred in a 
few months, from exhaustion, after several attacks of epilepsy. 



overwhelmed her with grief. In a few weeks her state became 
that of deep melancholia, in which she never alluded to her be- 
reavement, but was ever reproaching herself as sinful, unworthy 
to live, and deserving of eternal condemnation. She became 
insensible to all ordinary occurrences and atiections, indifterent 
to her family, inactive and silent, and attempted suicide. 



368 



ELEMENTAEY HYGIENE. 



The diseased depression of the feelings characteristic of 
melancholia may exist without impairing the intellectual opera- 
tions, but it is generally accompanied by delusions and hallu- 
cinations, although these usually derive their tone from the 
character of the disorder. They are insane explanations of the 
patient's wretchedness, or gloomy forebodings of what is to 
happen to him in the future. 

496. General Paralysis is defined to be a form of insanity 
characterized by a progressive diminution of mental power and 
by an incapacity which gradually increases and invades the 

• Fig. 132. 




GENERAL PAEALTSIS. 

Eepresents the physiognomy of a case of g-eneral paralysis — a raao. aged forty-eight, 
who had been insane three months before his admission to the asyhim. He had 
been destructive of clothing and violent to his wife, attempting to pull her ears off. 
He said it was his duty to kill her, and yet that he was always at prayer with her 
and for her. Although he would kick or scratch any patient -who inadvertently 
touched him, his general condition in the asylum w^as tranquil, verging gradually 
to mindlessness. ' He bad only in a modified degree the delusions of'grandeur ; 
he used to say he had a irold" watch and chain, and very fine clothes, bat they 
were in pawn. The portrait shows the curtain-like face, devoid of all expression, 
a perfect blank of thought and feeling The head is well shaped, and the features 
are handsome; but the amount of intellectual expression is less even than that 
displayed in the £ace of the idiot. 



whole muscular system. Its victims are generally men in strong 
health, from the better classes of society. " General paralysis 



FORMS OF MENTAL IMPAIRMENT. 369 

is emphatically the disease of manhood, for it is hardly ever 
met with before thirty, or after sixty ; the fact agrees well with 
the supposition that the sole cause of the disease may some- 
times lie in the agitation and anxieties incident to the most 
active period of life. Women seldom suffer from general 
paralysis." 

The earliest symptoms of motor derangement affect the 
tongue, and are evinced in thickness of speech and imperfect 
articulation of words, especially in those abounding with con- 
sonants ; as the disease advances, the muscles of the trunk and 
lower limbs are affected, and the walk becomes shuffling and 
tottering, articulation becomes more indistinct, the brows droop, 
the power of using the arms is impaired, the sphincters relaxed, 
and the patient may be choked to death by a lump of food 
sticking in the throat which he cannot swallow. 

It is a curious fact that the mental derangement accompany- 
ing this striking and fatal decay of bodily energy takes the form 
of an exaggerated feeling of personal power and importance. 
At first there may be manifested a lack of the usual energy ; 
but as the disorder increases, there come extravagant delusions 
of grandeur and capability of accomplishment. " The patient 
fancies himself possessed of wealth and power illimitable, and 
is often fantastically imaginative. One man imagines himself 
the possessor of ship-loads of gold and silver and precious 
stones ; another fancies himself greater than God ; another 
says he can lift the world, and that all the children that are 
born in all parts thereof issue from his loins. This man, also, 
says that he is heavier than the world, and that all the men in 
the world cannot lift him. We invite him to lie down, and 
lift him with ease ; he innnediately explains the tact that our 
success is owing to the buoyancy ot* the angels that are in 
him '' (Dr. Bucknill). 

497. Dementia. — This form of mental impairment consists 

in extreme debihty which results from loss, obliteration, or 

decay of the faculties. The lirst indication of its approach is 

loss of memory, especially as to recent events, the reason and 

16^' 



370 



ELEMENTAEY HYGIENE. 



judgment being still good witliin the sphere of distinct recol- 
lection. The second stage has been defined to be loss of judg- 
ment or an incapacity of ordinary reasoning. From this point 



Fig. 133. 




PEIMAEY DEMENTIA. 



Kepresents the aspect of a woman, aged forty, the victim of primary dementia. She had 
a severe attack of typhus fever when nineteen years of age, after which, her hus- 
band says, " ner jaw dropped and she has never been perfectly right since." She 
was admitted in a condition of extreme filth and personal neglect, and mentally was 
void of sensation, emotion, and thought. On her blank physiognomy there are 
no traces of passion, telling of former storms of mania ; there is not even the 
slightest effort of attention which corrugates the brow of the idiot. She never 
laughs, weeps, or indicates any annoyance; knows none of the attendants by 
name, and if she were not fed like an infant, would die of starvation. She is fat, 
has a good color, and the physical functions are performed well, affording a good 
example of the extent to which physical health may be retained when the activity 
of the cerebral functions is reduced to its lowest ebb. 



the malady may advance to the stage of incomprehension, the 
individual aftected being incapable of understanding the mean- 
ing of any thing said to him. The thoughts are incoherent and 
the determinations vague, uncertain, and aimless. The last 
stage is marked by the loss of all sense, volition, and even 
instinct, the victim of disease having sunk to a mere organic 
existence. 

Dementia is said to be primary when it is tlie first stage 
of the mental disorder, and develops itself directly by loss of 
memory, the power of attention, and executive ability. It is 



FORMS OF MENTAL IMPAIRMENT. 



371 



secondary^ or consecutive, when it appears as a consequence 
of other diseases. Insanity in its various forms often degener- 
ates into dementia. 



Fig. 134. 




SECONDARY DEMENTIA 

This likeness is of a woman, aged forty-nine, the subject of secondary dementia. Her 
insanity of two and a half years'* standinor began with acute maniacal excitement, 
with delusions of a religious type and suicidal desire. She thought that her soul 
was separated Irom her body, and that it was forever lost. She tried to strangle 
herself. After admission to the ai:ylum the violence subsided, and she passed into a 
state of chronic excitement, which has continued with gradually decreasing ment al 
powers. She holds imaginary conversations Vv'ith persons she has known in early 
life, an<l this hallucination has caused that earnest, inquiring look so faithfully 
given in the portrait. The general expression of the face is tliat of mindlcssness, 
combined with deep lines of emotional excitement which presents a m.'irked con- 
trast to the foregoing case of primary dementia. 

498. Idiocy. — This term is applied to that profound infirm- 
ity of the cerebro-spinal system which is due to arrested devel- 
opment before birth, or in early infancy, and which perverts 
or destroys the reflex, instinctive, and intellectual functions. 
Idiots arc incapacitated in their movements, senses, feeliniis, 
understanding, and w^ill. The characteristics of this condition 
arc manifested in different dcgTces. 

In the lowest form of idiocy there i?^ total mental vacuity. 
Its victim is deaf, dumb, and bUnd, without taste or smell, and 
is hardly alive to external impressions. The functions of or- 
ganic life are but ill-performed, the helpless creature being 



872 ELEMENTARY HYGIENE. 

below even the vegetable and he would perish but for the con- 
stant care of others. 

Tig. 135. 




IDIOCY. 

This cut is from a photograph of J. E., at the Eandall's Island House of Eefuge. He 
is twenty -four yeai-s of age, four feet seven and a half inches high, and weighs 
seventy-two pounds. His head is but fourteen and a half inches in circum- 
ference, its growth having been arrested at birth. Mentally he is a child, with 
only the faintest rudiments of intelligence. He knows his attendants and 
his name, and attempts to speak a few words, but is incapable of definite articu- 
lation. He feeds himself with a spoon, the food having been prepared for him. 
He shows his red cap with vanity, and is not without affection. He is usually 
passive and quiet, and gives but little trouble except when provoked; his feeble 
and torpid mind being only roused by external stimulation. His is a remarkable 
case of congenital idiocy, in which persistent efforts at improvement have accom- 
plished but little. 

A grade higher than this manifests imperfect sensation, 
feeble power of motion, and the dawn of intellectual and moral 
capacity. The idiot may be capable of moving about, shuns 
the cold, and gives notice of his desire for food, but recognizes 



FORMS OF MENTAL IMPAIRMENT. 373 

nobody and cannot help himself, while all his actions are with- 
out reflection or object. 

Then there are those, still more elevated in the scale, who 
begin to be conscious of their sensations, who recognize per- 
sons and objects to which they are capable of becoming attached. 
They have a feeble self- direction and employ signs, gestures, 
or cries, to make known their wants, or they may use badly- 
articulated words. 

The degradation of idiots is displayed in the vacant stare, 
everted lips, slavering mouth, irregular teeth, frequent strabis- 
mus, imperfect senses, defective speech, and uncertain, swaying 
walk. Their heads are generally, but not always, small, the 
smallest, however, appertaining to the most degraded. Idiotic 
heads are more commonly malformed, the skull assuming end- 
lessly-diversified shapes of contortion. 

• 499. Imbecility. — This term denotes a degree of mental 
deficiency not so low as that of idiocy — a development rather 
retarded than arrested. It is sometimes congenital, while idiocy 
is always so. The memory and understanding of the imbecile 
are in a state of feebleness, but they are capable of some educa- 
tion, and of acquiring various simple arts. Like idiocy, imbe- 
cility has its grades, some being so mentally torpid as only to be 
aroused by influences from without. " They cannot follow a 
conversation, still less a discussion. They regard as serious 
things the most gay, and laugh at those that are the most sad. 
They reply correctly, but you must not ask them too many 
questions, nor require from them responses which demand re- 
flection." They are equal to the performance of many of the 
ordinary duties of life, and are often able to take care of them- 
selves. Others display considerable shrewdness, and are con- 
stantly indulging in jokes ; they pass for half-witted people 
whose droll behavior and ready repartees create amuse- 
ment. 

With more mind and stronger impulses than idiots, but 
Avith imperfect self-control, inibooilos are more apt to be vicious. 
They are passionate and suspicious, and arc liablo to delusions 



374 ELEMENTARY HYGIENE. 

of the evil iutentions of others, which often make them dan- 
gerous. 

Fig. 136. 




IMBECILITY. 

Bepresepta a case of congenital imbecility in a youth ased twenty-seven. He is the 
son of a woak-minded father, and has always been of a weak mind. When first 
admitted he was dirty in his habits, restless and mischievous, but has become 
cleanly, quiet, and docile. His intellectual power is very low, and the likeness 
well represents the vacant, expressionless stare of imbecility. 

500. Degrees of Mental Impairment. — ^We have here 
briefly described the leading forms of mental disease, which, in 
their ultimate stages, dissolve the responsible relation of their 
victim to society. What to do with these cases is a question 
for the physician and the judge ; but from the point of view of 
Mental Hygiene, which aims at their prevention, our attention 
is drawn to the definite causes of mental impairment which are 
seen in many other effects besides those of overt insanity. 
There is much perverted mental action that never passes into 
mania ; much mental wealmess that never reaches dementia ; 
much morbidity of feeling that never ripens into moral insan- 
ity. The classes in which mental defects are so prominent 
that the State must assume their charge, are deplorably numer- 
ous ; yet they form but a fraction of the total amount of 



CAUSES OF MENTAL IMPAIRMENT. 375 

mental weakness and incapacity wliich exists in the commu- 
nity. Massachusetts reports three thousand insane, twelve 
hundred idiots, about five hundred blind, and four hundred 
deaf-mutes. But, besides these, she has ten thousand paupers, 
■ — persons incapable of taking care of themselves — and a large 
criminal class who, from moral perversity, in which low and 
deficient organization plays a leading part, become the scourge 
of society. And, besides these conspicuous cases of unhealthy 
mental constitution, there are scattered through society thou- 
sands more who are more or less disqualified for the duties of 
life by intellectual inability and moral weakness. No one can 
observe the inmates of a school-room without being struck by 
the very considerable proportion of those who are mentally 
deficient, backward, and stupid, or wayward, wilful, and vicious 
of temper. In the circle of our neighbors how many can be 
recollected who, by reason of mental deficiency, are practically 
incompetent and unfit for self-guidance and self-maintenance in 
the sharp conflicts and competitions of society. But whether 
the phenomena of mental impairment are total or partial, they 
are to be looked upon as due to the same general causes, and 
to these we will now give attention. 

Section III. — Causes of Mental Impairment 

501. Insanity the Result of Concurring Influences. — As 
the organ of the mind is the most delicate and complex of all 
parts of the living system, while its manifestations are so varied 
as to comprehend the whole circle of human thought and feel- 
ings, it is natural to snppose that the causes of cerebral impair- 
ment will be varied and complex in an equal degree. These 
causes are usually regarded as twofold, moral and 2)hi/sicaL 
The former are those which take efiect through the mind, as 
anxiety, over-study, or reverses of fortune ; the latter are those 
which act directly upon the physical system without the inter- 
vention of the mind, as blood-poisoning by fever or narcotics, 
or an injury to the head. Another division is into ^>/V(//.Ny>(Ks'- 
i)i(/ and exciting causes. Predisposing causes are such as act 



376 ELEMENTAEY HYGIENE. 

remotely, or by slow degrees, to undermine the mental health ; 
while exciting causes are those untov/ard events which imme- 
diately precede the breaking down of the mind. It is a com- 
mon error to assign some shock or calamity as the efficient and 
adequate cause of an insane outbreak, whereas the real caus- 
ality lies farther back, and the occurrence in question is only 
the occasion of its development. The germ of the insanity may 
have been deeply latent in the constitution, and a long train of 
influences may have been at work to impair the cerebral vigor, 
while some event, perhaps of slight importance in itself, serves to 
bring on the final catastrophe. When it is said that a person has 
become insane through disappointment or religious excitement, 
we are not to suppose that this is the whole statement : the 
question arises, how is it that others in quite similar circum- 
stances are unafiected ? The human mind is not so constituted 
as to snap by a sudden strain, like cast-iron ; insanity suddenly 
produced by the action of a single cause is of the rarest occur- 
rence. Only by a " conspiracy of conditions," internal and 
external, proximate and remote, is the fabric of reason usually 
overthrown. 

We will first notice the immediate physiological actions by 
which health of mind is destroyed, and this will prepare us to 
understand how the remoter causes of mental impairment take 
effect. 

502. Nutrition of the Cerebral Struetures.--If the mind 
is dependent upon the brain, it follows that each act of mind 
has its physical conditions, and this conditioning must of course 
be in accordance with the structure of the organ. The men- 
tal mechanism consists essentially of millions of cells and fibres, 
the former of which are the generators and the latter the trans- 
mitters of force. In thinking and feeling, these are called into 
exercise, and according to its intensity exhausted ; while their 
functional power is restored by nutritive assimilation. The 
structure of the parts being perfect, mental coherency, energy 
and health depend upon their perfect nutrition. On the other 
hand, disordered mental manifestations are due to incapacitated 



CAUSES OF MENTAL IMPAIRMENT. 377 

structures which are immediately caused by imperfect nutri- 
tion. It is here, in their disturbance of the nutritive operations 
of the brain, that most of the causes of mental impairment take 
effect. "We attribute a large share of mental disease to pa- 
thological conditions of the brain whose most prominent char- 
acteristic is defective nutrition of the organ. In a very large 
proportion of cases this deficient nutrition is manifested after 
death in an actual shrinking of the brain — a shrinking which is 
coextensive with the duration and the degree of the loss of men- 
tal power. This loss of power marks all instances of cerebral 
decay, and is consequently a condition of most chronic cases of 
excitement " (Bucknill and Tuke). 

The effect of impaired nutrition is to produce derangements 
of structure, and these take many forms in the various cases of 
cerebral disease. The microscope has done much to elucidate 
the pathological changes of the brain, but such is the maiTel- 
ous delicacy of the organ that microscopists are still intensely 
occupied in making out the subtle details of its normal struc- 
ture. Many physical indications of nervous disorder no doubt 
remain to be discovered ; but from the peculiar complexity and 
difficulty of the case, a large amount of infirmity of nerve-ele- 
ment will probably never be detected by physical means. Xu- 
trition results from a relation between nerve-tissue and the 
blood; the causes of its perversion are therefore to be sought 
in various disturbances of the circulation as well as in the nerve- 
element itself. 

503. Disturbance in the Cerebral Circulation. — Nutrition 
is dependent upon the supply of blood ; in the brain, perhaps, 
more closely than in any other organ. The gray substance 
of the cerebral convolutions which are devoted to the higher 
mental operations, is richly supplied with minute blood-vessels 
which impart to the cells the material of their renewal, and 
remove the waste products of their activity. The quantity 
and quality of the blood they transmit must therefore exert 
a determininor influence over the functions and hciilth of the 



d7o ELEMENTARY HYGIENE. 

504. Congestion and its Effects. — As mental action de- 
pends upon the intereliange taking place between the blood- 
capillaries and tlie nerve-cells, it follows that increased excita- 
tion and interaction of ideas is accompanied by increasing 
interchange and demand for more blood. Or if, from any 
cause, there is excessive brain ward determination of blood, 
the plethora of the capillaries gives rise to increased mental 
excitement. 

If this heightened activity is prolonged beyond due limits, 
and especially if the brain is weakly organized, a state of mor- 
bid congestion is induced, and over-stimulation is followed by 
stagnation of ideas, head-swimming, and emotional depression 
and irritability. " There are few students who are not practi- 
cally conversant with the slighter symptoms of cerebral conges- 
tion. Absorbed in some intellectual pursuit, the student's head 
becomes hot and painfal, and his brain even feels too large for 
his skull. "With exhausted powers of thought and attention, he 
retires at a late hour, as he hopes, to rest, but he finds that he 
cannot sleep ; or, if he does, his repose is unrefreshing and dis- 
turbed by dreams. An hour's freedom from thought before 
retiring to bed would have enabled the partly-congested brain 
to recover itself." 

The stagnation of the cerebral currents and imperfect re- 
moval of noxious products, with the irregularities of excitement 
and depression which are the results of frequent brain-conges- 
tion, produce defective nutrition, which tends to impair the 
soundness of the organ. 

505. Anaemia, or bloodlessness, the opposite state of con- 
gestion, produces similar mental effects. Insufficiency of healthy 
blood, whether caused by its actual loss from the system, or by 
poverty and dilution of the fluid through want of food, imper- 
fect digestion, or any of the numerous anti-hygienic influences, 
by impairing the nutritive powers, enfeebles the organ and 
pow^erfully predisposes to insanity. The impediment to cell- 
nutrition, though arising from an opposite cause to the state of 
congestion, produces similar mental effects. In hypersemia. 



CAUSES OF MENTAL IMPAIRMENT. 379 

with hot head and fulness of the cerebral vessels, the mental 
functions are discharged with slowness and difficulty. In 
anaemia, with pale face, cool head, and weak pulse, the cerebral 
organs are in a state of irritable weakness, easily excited to ac- 
tion ; the action, however, being powerless and irregular. 

"^ The blood itself may not reach its proper growth and 
development by reason of some defect in the function of the 
glands that minister to its formation, or, carrying the cause 
still further back, by reason of wretched conditions of life ; there 
is, in consequence, a defective nutrition generally, as in scrofu- 
lous persons, and the nervous system shares in the general deli- 
cacy of constitution, so that, though quickly impressible and 
lively in reaction, it is irritable, feeble, and easily exhausted. In 
the condition of anaemia we have an observable defect in the 
blood, and palpable nervous suffering in consequence ; head- 
aches, giddiness, low spirits, and susceptibility to emotional 
excitement, reveal the morbid effects. Poverty of blood, it 
can admit of no doubt, plays the same weighty part in the 
production of insanity as it does in the production of other 
nervous diseases, such as hysteria, chorea, neuralgia, and even 
epilepsy. The exhaustion produced by lactation is a well-rec- 
ognized cause of mental derangement ; and a great loss of blood 
during child-birth has sometimes been the cause of an out- 
break of insanity " ( Dr. Maudsley). 

506. Perversions of the Blood. — Although the blood is a 
compoimd of wondrour, complexity, and undergoing incessant 
change by active influx and drainage, yet in health its consti- 
tution is preserved in such exquisitQ balance, that the cerebral 
engine of thought and emotion is kept in harmonious and per- 
fect action. This harmony is disturbed not only by excess or 
deficiency of the vital stream, but in a marked degree by the 
presence in it of various impurities. Every grade of mental 
disease, from the mildest depression to the fury of delirium, 
may be produced by the accumulation in the blood ot^ the 
waste matters of the tissues. The presence in the blood, for 
example, of uncxcrcted bile, so aflects the nervous substance as 



380 ELEMENTARY HYGIENE. 

to engender the gloomiest feelings, from wliieh the individual 
cannot free himself, although he knows that the cause of his 
depression is not in the actual condition of external circum- 
stances, but is internal, and of a transient nature. But it only 
requires the prolonged action of this cause to carry this morbid 
state of nerve-element to that further stao^e of deoceneration 
which shall result in the genuine melancholia of insanity. So 
also the non-evacuation of urinary products in the blood of a 
gouty patient acts upon the brain to produce an irritability 
which the mind cannot prevent ; and this, too, if not arrested 
by medical resources, is liable to pass on to maniacal excite- 
ment. 

In like manner suppressed discharges, the morbid products 
of typhus and typhoid fevers, and organic poisons generated in 
the system by small-pox or syphilis, and not promptly elimi- 
nated, are often efficient causes of nutritive perversion in the 
brain which result in various forms of mental disorder. 

Various substances introduced into the blood, as opium, 
hashish, belladonna, take effect upon the brain, each per^^erting 
the mental functions in a manner peculiar to itself Ingested 
alcohol produces an artificial insanity, in which the various 
types of mental disease are distinctly manifested. Its first 
effect is a gentle stimulation and a mental excitement, such as 
often precedes an outbreak of mania. This is followed by a 
rapid flow of ideas, an incoherence of thought and speech, and 
an excitement of the passions, which disclose automatic dis- 
turbance and diminished voluntary control, as in delirium from 
other causes. A condition of depression and maudlin melan- 
choly succeeds, as convulsion passes into paralysis— the last 
scene of all being one of dementia and stupor. 

507. Nutritive Repair of the Brain. — But independent 
of the quantity or quality of the blood supplied to the brain, it 
is liable to certain conditions of exhaustion and nutritive de- 
generacy to an extent far greater than the other organs of the 
body. These other organs have various means of escape from 
overtasking ; if they cannot increase their power so as to en- 



CAUSES OF MENTAL IMPAIRMENT. 381 

dure the burden imposed, they can refuse to act, or throw the 
excess of labor upon some other part. Overtasldng the 
stomach destroys appetite, and the task is no longer imposed. 
If the muscular system is worked beyond its power, it does 
not itself break down, but the excessive strain is thrown upon 
the nervous system, which receives the injury. The overtasked 
lungs throw part of their burden upon the skin and liver, and 
the overworked liver is relieved by* the kidneys. But the 
economy of the organism aflfords the brain no vicarious 
relief; if overburdened, it must suffer alone. Excessive exer- 
tion of the brain produces an excitement, which, instead of 
ceasing, is augmented by the very debility which it causes. 
The exhaustion continues the overwork, which again increases 
the exhaustion. The degeneration of nerve-element thus pro- 
ceeds at a rapid rate of increase, which results in permanent 
perversion and degradation of the mental functions. 

The conditions of rest and nutritive renovation of the mind's 
organ are provided for in the mechanism of the solar system, 
by which the quietude of night, darkness, and silence alternates 
with the stimulation of light and day. The. recovery of its 
tone through nutritive repair undoubtedly takes place in the 
brain during the suspension of its functional activity in sleep. 
That sleep should be sound in quality and sufficient in quantity 
is one of the first conditions of mental health and vigor, and 
the want of it, as all have observed, reacts powerfully upon the 
state of the feelings. "The ill effects of insufficient sleep may 
be witnessed on some of the principal organic functions ; but 
it is the brain and nervous system that suffer chiefly and in 
the first instance. The consequences of a very protracted vigil 
are too w^ell known to be mistaken ; but many a person is suf- 
fering, unconscious of the cause, from the habit of iri'ogulnr and 
insufficient sleep. One of the most common effects is a degree 
of nervous irritability and peevishness wliich even the happiest 
self-discipline can scarcely control. That buoyancy of the 
feelings, that cheerful, hopefnl, trusting temper, which springs 
far more from oro-anic conditions than from mature and detinite 



382 ELEMENTARY HYGIENE. 

convictions, give way to a spirit of dissatisfaction and dejection • 
while the even demeanor, the measured activity, are replaced 
either by a lassitude that renders any exertion painful, or an 
impatience and restlessness not very conducive to happiness." 

Such are the eftects upon the healthy constitution of that 
slight disturbance of brain nutrition which accompanies insuf- 
ficient repose ; but when this state of things is much protracted 
or tates efiect upon a weakly-organized nervous system, the 
mental integrity becomes endangered. Sleeplessness is both a 
symptom and an immediate cause of cerebral disorder. Buck- 
nill and Tuke observe : " Want of refreshing sleep we believe 
to be the true origin of insanity dependent upon moral causes. 
Very frequently when strong emotion leads to insanity, it 
causes in the first instance complete loss of sleep." 

The quality of the sleep, moreover, that is, w^hether it be total 
or partial, is of the first importance. In painful and harassing 
dreams the emotional perturbation continues, and the individual 
awakens exhausted rather than invigorated. It is probable 
that in such cases, when the mind is abandoned to fantasy, 
and the control of the judgment is lost, the w^asteful activity of 
certain parts of the brain may exceed that of the waking state. 
Various cases are mentioned in w^hich patients have ascribed 
their attacks of mania to the influence of frightful dreams. 

We thus see in what mental impairment, in its various 
degrees, really consists. To the physiologist the question of 
healthy mental activity resolves itself into that of the sound- 
ness of nerve-element, and of the vigor and completeness of 
nutrition; w^hile mental impairment is seen to result from 
instability of the nerve-structures consequent upon defective 
nutrition. In this view, therefore, all causes, physical or moral, 
immediate or remote, which influence the nutritive operations 
of the system, have a bearing, more or less direct, upon mental 
conditions and character. 

We will now pass to some of the remoter influences by 
which mental health is impaired. 

508. Hereditary Transmission. — The living constitution 



CAUSES OF MENTAL IMPAIRMENT. i)H6 

is powerfully influenced by many slow-working agencies. The 
causes of mental deterioration produce efiects in time, and 
througli successive generations. Hereditary transmission thus 
becomes a leading factor in the problem of mental impairment, 
and accounts for many of the agencies by which it is produced. 

It is well known that like produces like in the organic 
world : the oak descends from a parent oak ; horses from an- 
cestral horses; characters are inherited; and thus the identity 
of each species is preserved. But while the distinctive ele- 
ments of the type are always transmitted, there is a tendency 
to variation in minor peculiarities. The child has a double 
origin, drawing its family traits from two different sources. 
It cannot inherit both sets of characters. The parental quali- 
ties may mingle equally in the ofl'spring, or the marks of one 
parent may predominate over those of the other, or even ex- 
clude them. Again^ the parents themselves have inherited the 
traits of their progenitors, and these may be more fully brought 
out in their offspring than in themselves, so that the child is 
made to represent many individuals. Thus, in the course of 
generations, by the blending of diverse stocks, special or family 
traits tend to fade away and disappear. Mental characters 
follow the same law as external features, although they are 
more obscurely indicated. 

Bodily defects and diseases are also transmissible. Con- 
sumption, gout, asthma, cancer, leprosy, scrofula, apoplexy, 
unsoundness of teeth, and even long-sight, short-sight, and 
squinting, are liable to be inherited. Of course these diseases 
are not transmitted in all cases of their occurrence, nor do they 
always pass directly from parent to offspring ; one or two gen- 
erations may be skipped, and the malady appear in the distant 
descendants. Hence, strictly speaking, it is not the disease 
that is hereditary, but a predisposition to it, which may either 
be neutralized and disappear, remain dormant, or break out, 
according to circumstances. 

There is, perhaps, no form of constitutional defect more 
markedly hereditary than morbidities of the nervous system. 



384 ELEMENTARY HYGIENE. 

Esquirol observes that of all diseases insanity is the most 
hereditary. The proportion of cases in which this malady 
is ascribed to predisposition, has been variously estimated at 
from one-fourth to nine-tenths; probably at least one-half of 
all these cases of disease have this origin. Extensive and care- 
ful inquiry has led to the conclusion that predisposition to in- 
sanity on the part of the mother is more liable to be trans- 
mitted to children than a like tendency on the part of the 
father, but it is the daughters that are most exposed ; the ma- 
ternal defect, while it is equally dangerous to the sops as the 
paternal, is twice as dangerous to the daughters. 

The common notion, that insanity is inherited only when 
madness in a parent reappears as madness in the child, is a 
most serious error. That which is transmitted is nervous 
infirmity, which may assume an endless variety of forms. 
Parental nervous defect may issue in one member of the 
family in unbalanced character, which is manifested in violent 
outbreaks of passion and unaccountable impulses, while another 
may go smoothly through life without exhibiting a trace of it, 
and. a third will break down into mania upon some trying 
emergency. As features are modified by descent, so are 
diseases, and none assume so wide a diversity of aspect as 
those of the nervous system. 

" If, instead of limiting attention to the individual, we scan 
the organic evolution and decay of a family — processes which, 
as in the organism, are sometimes going on simultaneously — 
then it is made sufficiently evident how close are the funda- 
mental relations of nervous diseases, how artificial the divisions 
between them may sometimes appear. Epilepsy in the parent 
may become insanity in the ofispring, or insanity in the parent 
epilepsy in the child ; and chorea or convulsions in the child 
may be the consequence of great nervous excitability, natural 
or accidental, in the mother. In families in which there is a 
strong predisposition to insanity, it is not uncommon to find 
one member afflicted with one form of nervous disease and 
another with another ; one suffers, perhaps, from epilepsy, 



CAUSES OF MENTAL IMPAIRMENT. SSd 

another from neuralgia or hysteria, a third may commit sui- 
cide, and a fourth become maniacal. General paralysis is a 
disease which is usually the result of continual excesses of one 
sort or another ; but it may unquestionably occur without any 
marked excesses, and when it does so there will mostly be dis- 
coverable an hereditary taint in the individual " (Dr. Maudsley). 

509. Debilitatedl Stock a Source of Criminality. — How 
the running down of stock through loss of vital power by 
hereditary influences should swell the ranks of the dependent 
classes, or those incapable of self-support, is obvious ; but this 
cause is equally powerful in reenforcing the dangerous classes 
who fill our jails and prisons. Immoral training and vicious 
associations are undoubtedly among the potent agencies by 
which these are educated for the career of vice and crime, but 
a cooperating cause of far greater power is low organization 
or defective cerebral endowment. They begin life with a ner- 
vous system incapable of the higher controlling functions. 
The children of paupers generally inherit a lack of bodily and 
mental vigor, while the offspring" of criminals have transmitted 
to them a disturbed balance of constitution — an activity of 
certain propensities, with a congenital weakness of the restrain- 
ing sentiments. Upon this point a writer of large observation 
and experience of these classes. Dr. S. G. Howe, observes : 

" There is a common opinion that in classes and individu- 
als of low organization the purely animal appetites are apt to 
be fierce and ungovernable, but it is not so ; on the contrary, 
as a general rule, the whole nature is let down and enfeebled ; 
and persons in this condition are docile and easily governed. 
Sometimes, indeed, there is fearful activity of the animal na- 
ture in persons of very low organization, which impels them to 
commit shocking outrages ; but these are exceptional cases, 
and the passions are usually the consequences of drink, or of 
insanity, rather than of intensity of nature. As a rule, in the 
classes marked by low and degenerate organization, the animal 
instincts and impulses are not stronger than in the others. On 
the contrary, the classes of higher bodily organization and 
17 



386 ELEMENTAEY hygie:n:e. 

vigor have more fire and potency even of animal appetites ; 
and their superiority comes, not from lack of impulses and 
temptations, but from greater activity and power of the 
restraining faculties of reflection and of conscience." 

In the light of these facts, the causes of mental impair- 
ment acquire a new and startling significance. The various 
agencies which are adverse to health not only shorten the 
duration of life, but they degrade its quality ; while dete- 
riorated life involves debilitated intellect and perverted 
moral powers. The general causes of impaired health which 
have been noticed, impure air, overcrowding in apartments, 
bad water, and insuflScient food, exposure to weather from 
inadequate clothing, want of exercise, or exhausting labor, 
and the whole array of bad physical conditions, by undermin- 
ing the bodily vigor and lowering the nutritive operations, be- 
come powerful and extensive causes of mental impairment, and 
stand in close relation to the evils and vices of society. Their 
baneful influence, how^ever, is not measured by their immediate 
effects upon the individual ; their power is multiplied by trans- 
mission, for they inflict upon his posterity the curse of a bad 
descent. Evil habits and bad conditions of life may not in the 
first case reach the extent of mental derangement, but they so 
impair the vital stamina that their victim bequeathes to his chil- 
dren enfeebled and degenerated nervous organizations, which 
are incapable of withstanding the strains and shocks of social 
experience. The lowered vitality and perverted nutrition of the 
parent become feeble-mindedness or insanity in the offspring. 

Hence, ''for the moral and intellectual elevation of the race, 
we are to look not exclusively to education, but to whatever 
tends to improve the bodily constitution, and especially the 
qualities of the brain. In our schemes of philanthropy w^e are 
apt to deal with men as if they could be moulded to any 
desirable purpose, provided only the right instrumentalities are 
used ; ignoring altogether the fact that there is a physical 
organ in the case, whose original endowments must limit very 
strictly the range of our moral appliances. But, v/hile we are 



CAUSES OF MENTAL IMPAIRMENT. 387 

brmging to bear upon them all the kindly influences of learn- 
ing and religion, let us not overlook those physical agencies 
which determine the efficacy of the brain as the material instru- 
ment of the mind " (Dr. Ray). 

510. Overtasking the Emotions. — Increase of insanity is 
undoubtedly a concomitant of advancing civilization. The 
savage state is marked by simple and unchangeable social insti- 
tutions, uniformity of manners and habits, limited wants, the 
discipline of privation, imperturbable resignation, feeble affec- 
tion, and few emotions. The savage rarely laughs and rarely 
sheds tears. The mental disorders, therefore, to which he is 
liable, correspond to his imperfect development; they are 
idiocy and imbecility — the mental diseases of children. On 
the contrary, in the civilized state there is a high and varied 
development of the emotions : all the circumstances of refined 
society conspire to intensify the feelings. Pride, ambition, 
fear, grief, domestic trouble, speculation, reverses of fortune, 
great successes, and great failures, exemplify the excitement 
and intoxication of the emotions to which a highly-civilized 
people are continually subjected. In this country the intense 
and universal passion for wealth, the periodical convulsions of 
politics, and the stimulation of free competition for place and 
profit, carry to a high point the strain upon the feelings. 
Worse than all, our education, instead of being a training to 
self-control, and a systematic discipline of the emotions through 
a calm cultivation of the sciences of Nature, is too generally 
conducted in the same spirit of excitement : studies are pur- 
sued under the spur of sharp competition for the prizes and 
applause of pubhc examinations, and, in place of sober and 
solid attainment, our culture degenerates into a mere prepara- 
tion for trade and politics. This state of things is far from 
favorable to mental stability. The victims of overtasked and 
perverted emotion fill our asylums, and it is impossible to view 
the increasing tendencies to social and public exoitomont with- 
out grave solicitude for its future cftccts. 

511. Overtasking the Intellect. — This is an extensive 



388 ELEMENTARY HYGIENE. 

cause of mental derangement, tliough perhaps less so than those 
just considered. The baneful efiects of cerebral exhaustion 
have already been noticed (507), and that study is often carried 
to this injurious length is notorious. Moderate use undoubt- 
edly develops and strengthens the brain, and it is equally cer- 
tain that if the amount of work is carried much beyond this 
point, the organ is endangered. Among the causes of insan- 
ity tabulated in insane asylum reports, excess of study figures 
as an inconsiderable item; but this belongs to the class of 
causes which mainly act by paving the way to a mental break- 
down. Cases like that of Hugh Miller, where, after an intense 
and protracted strain, the brain at last gives way, are by no 
means infrequent ; but in many an over-stimulated child or over- 
worked student there may be only sown the seeds of future 
mental disease, while other circumstances, such as loss of rest, 
grief, or disappointment, may cause the seed to germinate, and 
itself be taken as the cause, whereas it is in reality only the 
occasion. 

It has been objected to this view that the lunatic asylums 
are chiefly peopled with inferior rather than highly-cultivated 
minds ; but inferior minds are just those most likely to be in- 
jured by excessive study. The more highly developed the 
brain, the greater is its capacity of endurance. In his testi- 
mony before the Parliamentary School Commission, Dr. Car- 
penter announced his^ conviction, as a physiologist who had 
specially studied the question, that the children of the educated 
classes are capable, without injury, of twice as many hours of 
school-study as the children of the uneducated classes. 

What amount of labor the brain will endure without over- 
straining, depends upon various conditions, such as the age, 
original vigor of constitution, habits as to physical exercise, 
and intensity of application. The brain of the adult will bear, 
unharmed, an amount of labor which would be most injurious 
to a young person, and men of active habits can endure, with- 
out fatigue, mental application, which would be dangerous to 
the sedentary. Probably six hours a day of close brain-work 



CAUSES OF MENTAL IMPAIRMENT. 389 

is the maximum that the organ will endure without detriment. 
Mental labor may be prolonged, it is true, to double this length 
of time without apparent injury to the brain ; but in most cases 
the quality of the work performed will be found to indicate a 
lack of strength, vigor, and spontaneity. 

In order to disprove the unhealthfulness of this kind of 
exertion, attention has been called to the full ages reached by 
successful brain-workers who have achieved eminence in the 
various departments of mental activity. The collated results, 
however, have little value, for in the first place no one doubts 
that the cultivated brain is capable of a vast amount of labor, 
extending through a long lifetime, if judiciously exercised. 
In the second place, the biographies of eminent brain-workers 
actually show a vast amount of ill-health and suffering due to 
excessive study, while the number of those who achieve dis- 
tinction as thinkers, and then pass to premature graves as a 
consequence of it, is by no means small ; and in the third 
place, such a report is necessarily one-sided, as it deals only 
with the successes, and takes no account of the multitudes of 
failures of which the world never hears. 

It is not to be forgotten, however, that there are evils of 
mental under-action as well as of over-action. While there is 
no evidence that in the case of uncultured savages the brain is 
liable to become diseased from lack of exercise, the same thing 
cannot be affirmed of the cultivated races. The progress of 
civilization in these races is accompanied by a higher develop- 
ment and increasing complexity of cerebral organization, and 
this higher condition can only be maintained by a correspond- 
ingly higher degree of functional exercise. Without that activ- 
ity which its greater perfection implies and requires, the brain 
of the civilized man degenerates. A well-constituted organ 
demands exercise, and there can be no doubt that pleasurable, 
productive brain-work can be pui^ued to a great extent, in the 
form of close and severe mental labor, without injury. It is the 
evil accompaniments that genci*nlly work the mischief; the 
poisoning of the blood in the stagnant air oi close, unventilated 



390 ELEMENTARY HYGIENE. 

apartments ; the resummg of work directly after dinner, and 
prolonging it into the late hours of the night ; the provocation 
of stimulants and irregular habits ; the hard, repulsive task- work 
continued without recreation, and the unrelieved tension of 
anxiety that frets and strains and softens the delicate gray mat- 
ter of the brain, and ends at last in paralysis or imbecility. 

512. Early Sjrmptoms of Mental Impairment. — Of all 
the calamities to which man is liable, none is so appalling as 
the loss of reason, and when the diseases which cause it are 
far advanced, they are mostly beyond the reach of restorative 
measures. But a calamity so terrible does not come unheralded. 
Mental disease has its gradual beginning — its period of incu- 
bation, as the alienist physicians term it — ^which is accom- 
panied by various signals of impending difficulty ; and it is 
important that these early indications should be understood 
by all. 

One of the gravest warnings of approaching cerebral disease 
is debilitated attention and loss of memory. When an indi- 
vidual begins to fail in his customary power of keeping his 
mind to a subject, or forgets the names of familiar persons 
and objects, or is unable to make simple numerical calcula- 
tions with his usual facility and accuracy, or oddly transposes 
his words in conversation, there is serious ground for appre- 
hending softening of the brain or apoplectic seizure. Slight 
deviations of the facial features, the trifling elevation of an eye- 
brow, the drawing aside of the mouth a hair's breadth, or a 
faint faltering of the speech, are dangerous intimations of the 
advance of paralysis. 

The more active forms of mental disease have also their 
early symptoms. Preternatural acuteness of the senses, caus- 
ing exaggerations of sight, hearing, and smell, is the frequent 
precursor of a maniacal outbreak. The sensibility is not 
only exalted, so that the individual sees, hears, feels, and smells 
more keenly than in health, but it is often vitiated ; he sees 
double, agreeable odors become disgusting, and pleasant tastes 
offensive. A prickling sensation, or a sense of coldness, or 



CAUSES OF MENTAL IMPAIRMENT. 391 

grittiness in things touched, is sometimes experienced. In the 
case of a man who died of apoplexy, there was for some time 
previous to his illness a feeling in both hands as if the skin 
were covered with minute and irritating particles of dust and 
sand. 

The approach of mental disease is also foreshadowed in the 
conduct Singularity or eccentricity of deportment is not, in 
itself, to be taken as evidence of mental alienation. A large 
margin must be allowed for individual peculiarities ; there are 
naturally crooked sticks as well as straight ones. Whatever 
be the bent of the character, it is in the deviations from it 
that we are to watch for evidence of morbid action. But, 
when a person, who is well known to a circle of friends, begins 
to manifest unaccountable singularities of behavior; when a 
quiet and modest man becomes noisy and boastful ; when a 
habitually cautious man begins to embark in wild and reckless 
schemes ; when a person of a serious turn suddenly becomes 
hilarious, or one of a lively and buoyant disposition sinks 
into despondency ; when an affectionate person turns jealous 
and suspicious with no apparent reason, or one of usually 
steady industrious habits becomes idle, neglectful of business, 
and takes to running about — in such cases there is reason to 
believe that trouble is brewing. These deviations from cus- 
tomary habits *' are the switch-points which indicate that the 
mind is leaving the main line, and that, if left to itself, it will 
speedily career to destruction." 

Sometimes the earliest symptoms of cerebral derangement 
are manifested in the consciousness itself, and while no indica- 
tions of disorder are disclosed in the outward behavior, the in- 
dividual finds himself becoming the victim of morbid thoughts, 
which he cannot banish. A patient, waiting to Dr. C hoy no, 
observed : " I am not conscious of the decay or suspension oi 
any of the powers of my mind. I am as well able as over I 
was to attend to my business. My family suppose me in 
health ; yet the horrors of a mad-house are staring me in the 
face. I am a martyr to a species of persecution from within, 



392 ELEMENTAEY HYGIENE. 

wMch is becoming intolerable. I am urged to say the most 
shocking things ; blasphemous and obscene words are ever on 
my tongue." 

513. Hints and Precautions. — It is a serious error to sup- 
pose that, because there may be a predisposition to insanity in 
a family, therefore the members of it are to regard their danger 
in the light of a fatality from which there is no escape ; on the 
contrary, these are preeminently the cases in which, to a wise 
discretion, forewarning is forearming. The instances are prob- 
ably very few in which latent tendencies are developed into 
actual disease in spite of all precaution. It will generally be 
found that the outbreak is due to some immediate disturb- 
ing agency which might have been avoided. 

Where such a tendency exists, the education, occupation, 
and habits should be ordered with the strictest reference to it : 
the establishment of strong bodily health should be a para- 
mount consideration. The physical education should be 
specially directed to strengthen the nervous system and 
diminish its excitability. Much study, bodily inaction, con- 
finement to warm rooms, sleeping on feathers, are all favor- 
able to undue nervous susceptibility. 

In the education of children thus circumstanced, that is, in 
their brain-exercises, it is of the first importance to remember 
that whatever tends in any degree to impair the mental health, 
acts with redoubled power when cooperating with morbid 
tendencies. While the brain is yet plastic and pliable, a little 
mismanagement — ^the humoring of precocity, the repression of 
physical and nervous activity, or over-stimulation of thought, 
may awaken the germs of mental disorder, and lead to the most 
injurious consequences. 

To persons thus predisposed, steady and agreeable occupa- 
tion, which does not try the patience or the temper, or involve 
much responsibility, excitement, or exhaustion, is in the high- 
est degree desirable. Religious, political, and reformatory 
gatherings, where the passions are aroused and the sympathies 
excited, should be carefully avoided, together with all excite- 



CAUSES OF MENTAL IMPAIRMENT. O'Jd 

ments which tend to disturb the sleep. In respect to the mental 
habits, in such cases, Dr. Eay has the following excellent prac- 
tical suggestions : 

"Persons predisposed to mental disease should carefully 
avoid a partial, one-sided cultivation of their mental powers — 
a fault to which their mental constitution renders them pecu- 
liarly liable. Let them bear in mind that every prominent 
trait of character, intellectual or moral, every favorite form of 
mental exercise, is liable to be fostered at the expense of other 
exercises and attributes, until it becomes an indication of actual 
disease. Here lies tiieir peculiar danger, that the very thing 
most agreeable to their taste and feelings is that which they 
have most to fear. 

" There is another disposition of mind to be carefully 
shunned by the class of persons in question — that of allow- 
ing the attention to be engrossed by some particular interest 
to the neglect of every other, even of those most nearly con- 
nected with the welfare of the individuah The caution is espe- 
cially necessary in an age whose intellectual character is marked 
by strife and conflict, rather than calm contemplation or philo- 
sophical inquiry ; and in which even the good and the true are 
pursued with an ardor more indicative of nervous excitement 
than of pure, unadulterated emotion. The prevalent feeling is, 
that whatever is worth striving for at all, is worthy of all possi- 
ble zeal and devotion ; and, supported by the sympathy and 
cooperation of others similarly disposed, the coldest natures 
become, at last, willing to go as far and as fast as any. 

" Where the mind of a person revolves in a very narrow 
circle of thought, it lacks entirely that recuperative and invigo- 
rating power which springs from a wider comprehension of 
things, and more numerous objects of interests The habit of 
brooding over a single idea is calculated to dwarf the soundest 
mind ; but to those unfortunately constituted, it is positively 
dangerous, because they are easily led to this kind oi^ partial 
mental activity, and are kept from running into fatal oxtrotnos 
by none of those conservative agencies which a broader disci- 
17* 



394 ELEMENTAEY HYGIENE. 

pline and a more generous culture naturally furnish. The re- 
sult of this continual dvvelling on a favorite idea is, that it 
comes up unbidden, and cannot be dismissed at pleasure. Rea- 
son, fancy, passion, emotion — every power of the mind, in 
short — are pressed into its service, until it is magnified into 
gigantic proportions and endowed with wonderful attributes. 
The conceptions become unnaturally vivid, the general views 
narrow and distorted, the proprieties of time and place are dis- 
regarded, the guiding, controlling power of the mind is dis- 
turbed, and, as the last stage of this melancholy process, reason 
is completely dethroned." 

514. Medical Management. — Although diseases of the 
higher nervous centres, when they become seated, are, to a 
great extent, incurable ; yet, in their incipient stages, they are 
in most cases quite amenable to treatment. But, unhappily, 
those instances wliere delay is fraught with the greatest danger 
are, of all others, most liable to be neglected in their earlier 
stages. If the liver or the lungs get out of order, there is 
usually incontinent haste to consult the physician ; but if 
the very organ of reason is in danger of giving way, a mys- 
tery is made of it, and the dictates of common-sense are 
unheeded. 

IS'or is mere neglect the worst aspect of the case ; false 
notions of delicacy frequently become hinderances to early and 
decisive action. The ancient superstition, which connected 
insanity with special Providential disfavor, descends to U3 
in the shape of prejudices which speak of it still as a " taint," 
and lead to a culpable obliquity in dealing with it. Physi- 
cians of the largest experience attest that^ even when they are 
consulted in these cases, there is often the greatest difficulty in 
getting at the real conditions ; both the patient and his friends 
studiously concealing or flatly denying the facts. 

The progress of medical science and the impulses of public 
philanthropy have called into existence those noble institu- 
tions, where alone physical and moral medication can be best 
united, and which are generally administered by physicians of 



CAUSES OF MENTAL IMPAIRMENT. 395 

the largest experience in this department of practice. When, 
therefore, an individual begins to manifest symptoms which 
excite the apprehensions of his family or friends, no time 
should be lost in procuring the best professional advice and 
securing the advantages which those establishments offer ; and 
if the patient is placed in an asylum, the friends, remem- 
bering that time is generally an all-important element of re- 
covery, should largely trust the discretion of the medical super- 
intendent in regard to the proper duration of his confinement. 



QUESTIOI^S 



I'^I^T DP^IRST. 



CHAPTER I. 



1. How does science arise ? 

2. What makes science possible ? What are phenomena ? How are 
they divided ? What is the essence of scientific inquiry ? 

3. What is said of the connection of the sciences ? 

4. With what class of ideas does mathematics deal ? 

5. Of what does physics treat ? 

6. What makes chemistry possible ? Where should it come in the 
order of study ? 

V. What is biology ? How is it related to mathematics, physics, and 
chemistry ? What great questions are peculiar to it ? 

8. What are the divisions of biology ? 

9. With what order of facts does morphology deal ? What are its 
principal subdivisions ? How is it related to classification ? 

10. What is meant by distribution ? 

11. Of what does physiology treat ? What are its subdivisions ? ^ 

12. What is etiology ? 

13 and 14. Why should physiology be studied ? 

CHAPTER II. 

15. How are the bodily actions studied ? 

16. What facts may we thus obtain ? 

17. Describe the ice-chamber experiment. What does it show ? 

18. How is the strength restored and the loss made good ? 

19. In what form is matter excreted from the body ? 

20. What is said of the absorption of oxygen ? 

21. What is meant by the physiological balance? 

22. How may it be maintained ? What conditions disturb it ? 

23. What determines the amount of force set free ? 

24. Give an outline of the bodily structure. 

25. Describe the vertebral column. What cavities do the bodies of 
the vertebrae separate ? 

26. What does the spinal canal contain ? How is the ventral cavity 
divided ? What canal traverses the two ventral chambers ? What else 
does the abdomen contain ? What the thorax ? 



QUESTIONS. 397 

27. Describe the head. What are contained within its cavities ? 

28. What does a longitudinal section prove ? What is shown by 
transverse sections ? What is said of the limbs ? 

29. Describe the layers of the skin. 

80. How does the skin differ from mucous membrane ? 

31, What is connective tissue ? 

32. What is said of the muscles ? 

-^ 33. What constitutes the skeleton ? How many bones does it con- 
tain ? How are they fastened together ? 

34. What enables us to stand upright ? 

35. What of the relation of the mind to the muscles ? 

36. What organs control the actions of the muscles ? What special 
power does the cerebro-spinal axis possess ? 

37. What is meant by " special sensations " ? Name the organs which 
receive only certain kinds of impressions ? What are they called ? 

; 38. What is said of the renewal of tissues ? 
.f 39, What are the organs of alimentation ? 
/ 40. Name the organs of distribution, 
I 41, What is meant by the exchanges of the blood ? 

42. Name the principal excretory organs. In what respects do they 
resemble each other ? 

43. What important additional purpose do the lungs fulfil ? 

CHAPTER III, 

44. Describe the capillaries. What is their function ? How are they 
distributed ? 

45. Of what are the capillaries continuations ? How do they differ 
from the small arteries and veins ? How are the muscles of the small 
arteries disposed ? 

46. What does their contraction effect ? 

47. How is their contraction re<2;ulated ? 

48. Wherein do the arteries and veins differ ? 

49. Describe the valves of the veins. How may their action be 
demonstrated ? What arteries possess valves ? 

60. Describe the lymphatics. Where are they distributed ? Where 
do they discharge their contents ? 

51. What are the lacteals ? What is their function ? 

52. What large trunks pour venous bloo^l into the heart ? From what 
great trunk do most of the arteries spring ? What vessels carry blood to 
and from the lungs ? Into what parts of the heart do these various trunks 
open ? 

53. What vessels supply the substance of the heart ? 

54. AVhat great vessel carries venous blood from the abdominal viscera 
to the heart ? Through what great organ does it ramify ? 

55. What is the average size of the heart ? What its shape and posi- 
tion ? By what membrane is it enclosed ? 

56. Describe the cavities of the heart. What are tliev called ? 

57. What is their relative amount of work ? 

58. What tissue mtikes up the walls of the heart ? What membrane 
lines the cavities of the heart? How are the conmuiuicaling apertures 
strengthened ? What are attached to these rings ? 

59. Describe the structure and attachments o{ tlie heart-valves. What 



398 QUESTIONS. 

valves close the right auriculo-ventricular aperture ? What the left ? 
How are the free edges of the valves supported ? What is the action of 
these valves ? What valves are situated at the commencement of the 
aorta and pulmonary artery ? What is their action ? How may the 
action of the valves be demonstrated ? 

60. What is said of the rhythm of the heart ? What is meant by 
" systole " and " diastole " ? 
^^ .^ 61. Describe the working of the heart. 
62. What is the action of the arteries ? 
/ 63. What constitutes the beat of the heart ? 
^ 64. What is said of the sounds of the heart ? 

65. What constitutes the pulse ? 

66. Why does the blood jet from cut arteries ? 

67. Why are the capillaries pulseless ? 

68. How do the subdividing arteries affect the flow of blood ? 

69. What causes the steady capillary flow ? 

70. Trace the course of the blood from the right auricle. How is the 
y heart itself supplied ? 

/^ 71. What is the shortest complete circuit the blood can make ? The 

( longest ? 

72. How does the nervous system affect the circulation? 

73. What happens in blushing ? 

74. How may this be proved ? 

75. What relation has this nervous control to disease ? 

76. What relation does the heart bear to the nervous system ? 
7^. How may the movements of the heart be directly observed ? 

78. What is the proof that the blood circulates ? 

CHAPTER IV. 

79. How may we obtain blood for examination ? 

80. How does it appear to the naked eye ? How under the pocket 
lens ? 

81. What takes place when a drop is left to itself ? What is the effect 
, of salt upon it ? 

y^~ 82. How many kinds of corpuscles does the blood contain ? 

/ S3. Describe them. 

1 84. What is the structure of the red corpuscles ? 

85. What are the peculiarities of the white corpuscles ? 

86. How may the real nature of the corpuscles be determined ? 

87. What is supposed to be their origin ? What is said of the cor- 
puscles of the lower animals ? 

88. What occurs to the corpuscles when the blood dies ? • 

89. How are blood-crystals formed ? 

90. What is meant by coagulation ? 

91. Into what constituents does the blood separate ? 
' 92. What is the buffy coat ? 

93. What conditions influence coagulation ? 

94. What is the nature of the process ? 

95. What causes the blood to coagulate? 

96. Name some of the physical properties of the blood. 

97. What is its chemical composition ? 

98. How does age influence the blood? Sex? Food? 



^•v\\ 



QUESTIONS. 399 

99. What is tbe total amount in the body ? 

100. What is the function of the blood? To what does it owe its 
vivifying influence ? 

101. What is said of the transfusion of blood ? 

102. What of the lymph ? 

CHAPTER Y. 

103. What gives the blood its complex composition ? 

104. How is the blood changed in the capillaries? 

105. In what respects do arterial and venous blood differ? 

106. What is said of the diffusion of gases ? 

107. Why does the blood change color ? 

108. How is this change explained? 

109. Describe the capillaries of the lungs. 

'- 110. Trace the air-passages from the mouth to the air-cells. 

111. What is said of this mechanism? 

112. What are inspiration and expiration ? 

113. State the difference between inspired and expired air. 

114. What quantity of air passes through the lungs in 24 hours? To 
what extent is it vitiated ? How much carbon and water is eliminated 
in 24 hours ? 

115. What mechanism carries on the respiratory movements ? What 
is said of the elasticity of the lungs ? 

116. How do the bronchial tubes facilitate the movement of air? 

117. Describe the action of the chest-walls. Explain the action of the 
intercostal muscles. 

, . 118. What is the diaphragm ? Explain its action. 

119. What occurs when the diaphragm acts alone? What, if only 
the chest-walls are brought into play ? 

120. What other muscles aid the process ? 

121. How does the respiration differ in the sexes? 

122. What is meant by residual air ? Supplemental air ? Tidal air? 

123. What constitutes the stationary air ? What part does it play in 
respiration ? 

124. What is the composition of the stationary air ? 

125. How is the nervous system related to respiration? 

126. In what are respiration and circulation analogous ? 

127. What are the secondary phenomena of respiration ? 

128. What is said of the respiratory murmurs ? 

129. How does respiration assist the circulation ? • 

130. What are the facts relating to this point ? 

131. How does expiration affect the circulation ? 

132. How may the action of the heart be arrested ? 

133. What circumstances modify the respiratory function ? 

134. What occurs when a man is strangled? 

135. How is life destroyed by this means ? 

136. What is said of respiratory poisons? 

137. What is slow asphyxiation ? 

138. Why is ventilation so important ? 

CHArTEU YI. 

139. Describe the distribution of arterial blood throughout the body. 

140. What great organs are constantly draining the blocd ? 



400 QUESTIONS. 

141. What is said of its losses in the liver and lungs ? 

142. What are the intermittent sources of loss and gain to the blood? 

143. Give the position and anatomy of the kidneys. 

144. In what respects are the lungs and kidneys alike ? 

145. What is the composition of the renal excretion ? What is its 
average daily amount ? Its average of specific gravity ? 

146. Describe the structure of the kidney. 

147. What is said of its filtering mechanism ? 

148. From what source are the kidneys supplied with blood ? How 
do they change the blood ? 

149. How is the excretory action of the kidneys controlled ? 

150. What does the blood lose through the skin ? 

151. What quantity of matter is thus lost? What is the composition 
of the sweat ? 

152. Give thie conditions of its escape. 

153. What is said of the sweat-glands? What of their distribu- 
tion? 

154. How is the action of the sweat-glands controlled ? 

155. What conditions increase the amount of perspiration ? 

156. In what respects are the lungs, kidneys, and skin alike? 

157. What does the blood lose in the liver ? What does it gain ? 
Describe the liver. With what great vessels is it connected? Give its 
internal anatomy. What route does the blood take in its passage through 
the liver ? What is said of the liver-cells ? 

158. What is their function ? 

159. What is the daily quantity of bile excreted? Its composition? 

160. What becomes of the bile ? /^ A^A-A/V%^ 

161. What organs furnish the blood with oxygen? ■' 

'-• 162. What does the blood gain in the liver? What does it lose? 

163. How may the sugar-forming power of the liver be proved ? 

164. What does the blood gain from the lymphatics ? What of the 
" ductless glands " ? 

165. What is said of the spleen ? What is its supposed function? 

166. Through what channels does the body lose heat ? What is the 
source of bodily heat ? 

167. How is the heat of the body equalized ? 

168. How does evaporation affect the temperature ? 

169. What relation has the nervous system to temperature? 

170. What is said of the action of the glands ? What is the duct of a 
gland ? What are racemose glands ? What determines the activity of 
certain glands ? 

171. In what way are the salivary glands called into action ? What is 
the character of their secretion ? 

172. What does the blood gain from the muscles ? 

CHAPTER YII. 

173. What is another great source of gain to the blood ? 

174. How much solid material does a man daily receive ? How much 
oxygen ? 

175. What is the daily loss of dry solids? In what shape does the 
balance leave the body ? 

176. How ate foods classified ? What are Proteids ? Give examples. 



f 



QUESTIONS. 401 

What is the composition of fat ? What are Amyloids ? Give some ex- 
amples. What is meant by " vital fbod-s tuffs " ? What are mineral food- 
stuffs ? 

177. What is the composition of the vital food-stuffs? The mineral 
food-stuffs ? What constitutes a permanent food ? 

178. What occurs if protein is not supplied? What is said of the ne- 
cessity of other food-stuffs ? 

179. What is meant by nitrogen starvation ? 

180. 181. What are the disadvantages of a purely nitrogenous diet? 
^"'-'182. Why is a mixed diet desirable ? 

183. What constitutes a mixed diet? 

184. What is said of the intermediate changes of the food? 

185. What are the objections to the ordinary classifications of food ? 

186. What is the purpose of the alimentary apparatus ? 

187. Describe the cavity of the mouth and pharynx. What organs 
do they contain? Name the openings into the pharynx? 

188. Give the names and positions of the different salivary glands. 
How does the saliva affect the food ? 

189. Describe the teeth. 

190. Describe the working of the jaws. 

,^ 191. What occurs to the food during mastication ? Describe the 
operation of swallowing. 

192. How are fluids swallowed ? 

193. Describe the stomach. What is -the character of its lining mem- 
brane? What glands does it contain ? What fluids do these glands pour 
out ? What are the properties of the gastric juice ? 

194. What is meant by artificial digestion? 

195. By what routes does the food leave the stomach? 

196. What is said of the intestines? How are they divided ? Where 
is the ileo-csecal valve situated ? What is the caecum ? The vermiform 
appendix ? 

197. What glands are found in the intestinal mucous membrane ? 
What other structures ? 

198. What is peristaltic contraction? 

199. What glands pour their secretions into the duodenum ? What 
is said of the chyme ? 

200. What is chyle ? How does it differ from chyme ? What changes 
does the chyme undergo in the intestine ? AVhat juices effect this change ? 
In what way does the chyle reach the blood ? 

201. What is going on in the large intestine ? 
/ ./ 



/!^4/i4/^r^^,f: 



CHArTER YIII. 



202. What is meant by the " vital eddy " ? What maintains the 
active powers of the body ? 

203. In what way are the activities of the body manifested ? What is 
locomotion ? Name the organs of motion. 

204. Describe the cilia. How do they act? ^yho^e are they situ- 
ated? 

205. How do the muscles give rise to motion ? Into what two groups 
may the muscles be divided ? 

206. What muscles are not attached to solid levers ? What is tlie 
character of their fibres ? What is said of their contractions ? 



(. 



402 QUESTIONS. 

207. What muscles are attached to solid levers ? What is a lever? 

208. How many orders of levers are described ? What is a lever of 
the first order? Of the second order? Of the third order ? 

209. What levers of the first order are found in the human body? 

210. What of the second order? 
X ,211. What of the third order ? 

1 212. How may a single part of the body represent the three kinds of 
levers ? 

213. How many kinds of joints are found in the human body? 

214. Describe the structure and movements of a perfect joint. 

215. What are ball-and-socket joints ? 

216. What are hinge-joints ? 

21Y. What is a pivot-joint? Give an example from the human body. 

218. Describe the bones of the fore-arm. How are they articu- 
lated together ? What is meant by pronation and supination? 

219. What are Hgaments? How do the ligaments diifer in the differ- 
ent joints ? What is said of the hip-joints ? 

220. What different movements are the joints capable of executing? 

221. How are these movements effected? In what way are they 
limited ? 

222. What is meant by the origin and insertion of a muscle? How 
are the muscles attached to the bones ? What direction does the axis of 
a muscle usually take ? The exceptions ? 

223. Describe the operation of walking. 

224. When does a man walk with least effort ? 

225. What is said of running and jumping ? 

226. What conditions are essential to the production of voice ? 

227. Describe the vocal chords. To what are they attached? 

228. What cartilages enter into the structure of the larnyx ? 

229. Describe the muscles of the larynx. What does their action 
effect ? How are musical notes produced ? 

230. When will the musical note be low ? When high ? Upon what 
does range of voice depend ? Upon what the quality of voice ? 

231. What is speech ? How is the voice modulated? What is said 
of the vowel sounds ? What of consonant sounds ? 

232. What sounds require blocking of the air-current ? 

233. AVhat are explosive consonants ? 

234. How are speaking-machines constructed ? 

235. What is said of tongueless speech ? What example is given ? . 

CHAPTER IX. 

236. How are the muscles made to contract ? 

237. What calls the nerves into action? 

238. What is reflex action ? What is a sensation ? With what are 
sensations classed ? 

239. What are subjective sensations ? 

240. What is said of the muscular sense ? How may its existence be 
demonstrated ? 

241. What is said of the higher senses ? 

242. Give the general plan of a sensory organ. 

243. Where is the organ of the sense of touch located ? What are 
papillae ? What is a lactile corpuscle ? 



7 



QUESTIONS. 403 

244. What is interposed between it and external objects ? 

245. What is said of varying lactile sensibility ? 

246. What gives rise to the feelings of warmth and cold ? 

247. Where is the organ of the sense of taste found? Describe the 
papillae of the tongue. 

248. Where is the organ of the sense of smell located ? Describe the 
nasal passages. The nasal chambers. What do these nasal chambers 
contain ? 

249. How are odors brought in contact with the olfactory apparatus ? 

250. Where is the organ of hearing situated ? Of what does it essen- 
tially consist ? What bodies are found in the membranous labyrinth ? 
In the scala-media ? 

^ 251. What part of the ear is called the vestibule? What are the 
semicircular canals ? What the ampullae ? What fluids form a part of 
the mechanism ? 

252. Where is the scala-media situated ? What part is known as the 
scala iympani ? The scala vestibuli ? What peculiar mechanism is found 
within the scala-media ? 

253. What is the bony labyrinth ? What fenestrae does it contain ? 

254. What part of the ear is known as the drum ? How is this sep- 
arated from the external meatus ? In what way does the drum communi- 
cate externally ? 

255. What are the auditory ossicles? What two points do they con- 
nect ? What is their purpose ? How are the perilymph and endoiymph 
set vibrating ? 

256. What muscles are connected with the tympanic membrane ? 

257. What is the concha ? 

258. What conditions are necessary to the production of sound ? 
How is sound transmitted to the ear ? 

259. How do the aerial vibrations affect the tympanic membrane ? 
Into what two kinds of vibrations may bodies be thrown ? 

260. Which are supposed to transmit the impulses of the aerial 
waves ? 

261. Describe the actions of the auditory muscles. 

262. What part of the ear is supposed to take cognizance of the in- 
tensity of sounds? What part is concerned with the quality of sounds ? 

253. What is the probable function of the fibres of corti ? 

264. What is the purpose of the eustachian tubes ? 

CHAPTER X. 

265. What part of the eye is called the retina? 

266. What is seen on the centre of the retina ? 

267. Describe the microscopic structure of the retina. 

268. What is the function of the retina ? What is said of the sensa- 
tion of light ? 

269. In what respects do different parts of the retina differ? What 
is the blind spot? 

270. What is said of the duration of luminous inipiossions ? 

271. Can the retina become exhausted? What aie eoniplimontary 
colors ? 

272. What is color blindness ? 

273. What appearances are produced by pressure upon the eyeball. 



404 QUESTIONS. 

214. What is the function of the rods and cones ? What are Pur- 
kinje^s figures ? 

275. What physical agent gives rise to vision ? What is a convex 
lens ? Describe the experiment with the candle and lens. 

276. What is meant by the "focus"? What is adjustment of the 
eye ? When does the lens give a distant picture ? What is the efl'ect 
of moving the object ? 

\^^-~^ 277. What follows from varying the convexity of the lens ? What 
-^ relation does convexity bear to the focus? How does a convex surface 
I affect the rays of light? Describe the experiment with the watch-glass 
^ and water-box. What is a camera obscura ? 

278. What organs must the light pass through to reach the retina ? 
Give the structure of the eyeball. 

279. What are the humors of the eye ? By what organ are the 
humors separated ? Describe the crystalHne lens. 

280. Describe the choroid coat ? What is its position ? Where are 
the ciliary processes situated? 

281. Describe the iris. Where is it situated? What of the ciliary 
muscle ? What relation has the iris to the lens ? 

282. How does the eyeball resemble a water-camera ? 

283. How is the focus adjusted in a camera obscura ? How in the eye ? 

284. Describe the experiment. What does it show ? 

285. What is said of the mechanism of adjustment ? What are the 
facts of adjustment ? What explanations of the process have been offered ? 
Which is the most probable ? 

286. What limits the power of adjustment ? 

287. Name the muscles of the eyeball. What are their respective 
positions ? What does their action effect ? 

288. Describe the structure of the eyelids. What muscles move 
them ? 

289. Where is the conjunctiva situated? Describe the lachrymal ap- 
paratus ? What is the source of the tears ? 

290. What is meant by a simple sensation ? What is the character 
of most of our sensations ? 

291. What sensations are the simplest? 

292. Of what does a tactile sensation consist ? 

293. What is said of complex sensations and judgments ? 

294. Why are delusions of the senses impossible ? What is said of 
delusive judgments ? 

295. What are subjective sensations ? What examples are given ? 

296. Relate the case of Mrs. A. What senses were impUcated ? To 
what class did her peculiar sensations belong ? 

297. What conditions seemed to favor their development? What 
prevented her forming false judgments ? 

298. Were her senses really at fault ? 

299. How many outside causes give rise to delusive judgments ? Give 
an example. 

300. What is said of optical delusions? 

301. What is meant by the optic axis? How is the position of a 
phosphene accounted for ? 

302. What is said of the inversion of visual images ? 

303. How do objects and their visual *images correspond in number ? 
What is the action of multiplying glasses ? 



QUESTIONS. 405 

804. Upon what does perspective depend ? 
^ 305. How does the distance of an object affect its visual image ? How 
do convex and concave glasses affect it V 

806. Why do the sun and moon look larger near the horizon ? 

807. What is said of the judgment of form by shadows ? 
308. What is the principle of the thaumatrope? 

809. What is the explanation of squinting ? 

310. Give the principle of the pseudoscope, 

311. What of the stereoscope ^ 

CHAPTER XII. 

312. Of what is the bulk of the nervous system made up ? 
^,313. What two systems constitute the nervous apparatus ? 

""^ 314. Where is the cerebrospinal axis located ? What membrane sep- 
arates it from the bone ? What other membranes surround the brain 
and cord ? 

315. Describe the spinal cord. How is it divided? Describe the 
roots of the spinal nerves. ^ 

316. What does a transverse section of the cord show ? 

317. What follows the irritation of a spinal nerve ? 

318. What are the functions of the anterior and posterior roots? 

819. What results from cutting the anterior root of a spinal nerve? 
The posterior root ? Both roots ? 

820. How are impressions propagated along the nerves ? What is an 
afferent nerve ? 

321. What is negative deflection? 

822. What occurs when the spinal cord is cut across ? What when 
the end remote from the brain is irritated ? 

328. What power does the cord possess independenlly of the brain? 

324. What is said of the distribution of reflex effects? 

325. Do all parts of the cord possess a hke conducting power ? 
826. What is said of the conducting power of the gray matter ? 
327. What special functions have certain regions of the cord ? 

828. Describe the medulla oblongata. What cavity does it contain ? 
What overhangs this cavity? What is the pons varolii? Into what 
parts do the fibres of the medulla pass ? What elevations are found be- 
tween the crura-cerebri ? Where is the third ventricle situated ? Into 
what masses of nervous matter do the crura-cerebri pass ? Where is the 
pineal gla7id located ? T\\e pituitary body ? Where are iho lateral ven- 
tricles situated ? What forms the floor of the lateral ventricles ? What 
is said of the hemispheres of the brain ? How are they connected ? Wliat 
is said of the outer surfiices of the hemispheres ? 

329. How are the white and gray matter arranged in tlio medulla ob- 
longata? In the cerebellum and cerebral iiemisphores ? 

330. How many pairs of nerves are i2;iven off from the brain ? X;inie 
the first pair. The second. The third. In what muscles is the third 
pair distributed? Where are the fourth and sixth pairs distributed? 
Describe the origin and distribution of the tilth pair. In wlu.t nuiscles 
does the seventh pair terminate ? Th.e eighth pair torminate ? What 
is the function of the ninth pair? What organs does the tenth pair su^v 
ply? Describe the course of the eleventh pair. Give the origin and dis- 
tribution of the twelfth pair. 



406 QUESTIONS. 

831. What is said of the olfactory and optic nerves ? 

332. What effects follow injuries of the medulla oblongata ? 

333. What direction do the afferent impulses take in the medulla ob- 
/ longata ? Give the course of the fibres in the anterior pyramids. What 
1 would be the effect of dividing one of the crura-cerebri ? 

334. What is the function of the cerebral hemispheres ? 

335. What is sdd of the reflex action of the brain? 

336. What takes place in reading aloud ? 

337. What is meant by " artificial reflex actions " ? 

338. What is said of the sympathetic system ? 

CHAPTER XIII. 

339. What is said of the microscopical analysis of the tissues ? 

340. What is the early primitive structure of the body ? 

341. What is the character of the epidermis and epithelium? How do 
these tissues grow ? What is squamous epithelium ? What kind of 
epithelium lines the alimentary canal ? What is ciliated epithelium ? 

342. From what kind of tissue are the nails developed ? 

343. Of what are hairs composed ? Describe their growth. How are 
the hairs kept supplied with oil ? What is meant by horripilation^ or 
"goose skin"? 

344. What is the structure of the crystalline lens ? 

345. Of what is cartilage composed ? 

346. What is the structure of connective tissue? How is it affected 
by being boiled in water? How does acetic acid affect it? Of what are 
ligaments and tendons composed? What \?> fihro-cariilage ? 

347. Describe fat-cells. 

348. What are pigment-cells ? 

349. Describe the minute structure of bone. What are lacuuce? 
Conaliculi? What were the lacunar once supposed to be? Describe 
the Haversian canals. What is periosteum? What is found in the 
cavities of the bones ? 

350. How do bones grow? AVhat are sutures? In what kind of 
material are bony matters first deposited ? What is meant by centres of 
ossification ? 

351. Of what are the teeth composed ? Name the different parts of a 
tooth. What is the character of dentine? What is the structure of 
enamel ? 

352. How are the teeth developed ? Which are the deciduous, or 
milk teeth ? When do they appear ? 

353. How are the permanent teeth formed ? How divided ? When 
do they begin to appear ? How long before the set is completed ? 

354. What two kinds of muscles are found in the body ? Of what 
are the striated composed? What is a fascia? The sarcolemrna? 
What does it enclose? Of what is the contractile substance made up? 
What is the structure of smooth muscle ? 

355. What are the elements of nerve tissue? Describe the structure 
of a nerve fibre. How do the nerve fibres terminate ? 

356. What is a tactile corpuscle ? What is the structure of the olfactory 
nerves ? 

357. W\iQVQ2iVQ ganglionic corpuscles iQ\m&'i What is their structure ? 



r 



QUESTIONS. 407 



CHAPTER XIV. y 

858. What is said of the twofold value of knowledge? 

859. What is meant by " practical knowledge" ? 

860. Of what practical value is a knowledge of physiology ? What is 
said of its importance ? 

861. What were some of the old notions regarding disease V How 
did such views affect the community ? 

862. What is the true idea of health and disease ? How is this illus- 
trated in the case of gout ? 

868. When do the agencies of health become sources of disease ? 
What is the chief value of hygienic knowledge ? 

864. Name some of the results that have followed its application. 

865. What is said of its value as a remedial means ? 

866. How must it necessarily affect the actions ? 

CHAPTER XV. 

867. Give the constitution of the atmosphere. How is it rendered 
impure ? 

868. How do atmospheric impurities affect the senses ? 

869. What is said of carbonic acid as an impurity ? In what propor- 
tion is it thrown out from the lungs ? From what other sources does the 
air of apartments receive it ? 

870. What is the effect of air saturated with moisture ? Of dry air ? 

871. In what form is organic matter found in the air? What are 
some of its sources ? By what means may we determine its presence ? 
What is said of its presence in the air of sick-rooms and hospitals ? How 
does it affect the system ? 

372. What is said of the air of cellars ? 

378. How does air contaminated by certain trades affect the health ? 

874. What effect has impure air upon the scrofulous ? Relate the 
case of the Norwood school. 

875. What relation has an impure atmosphere to the spread of dis- 
ease ? 

376. How does impure air affect the course of disease ? What is of 
first account in the treatment of febrile complaints ? 

877. How are consumptives influenced by impure air ? 

878. How does bad air affect inherited taints ? 

879. What is its effect upon the mind ? 

880. How does nature purify the air ? 

881. What is the object of ventilation? IIow miiy pure air bo ob- 
tained ? 

382. What should be the standard of purity in air ? Give the ostimatos. 

883. How should the air be heated, and why ? 

384. What must be attended to iu regulating the movomont of the 
air? 

885. When are other means of purification required ? What sub- 
stances are most efficient as disinfectants ? 




408 QUESTIONS. 

CHAPTER XYI. 

886. What proportion of water do the various tissues contain? 

887. What duties does it perform ia the economy ? 

888. What leading property fits it for this office ? 

889. The average daily consumption of an adult ? 

890. What is said of its excretion ? 

891. What gives rise to the several varieties of water. 
392. What is said of soft water ? 

893. How is hard water formed ? 

894. AVhat are mineral waters ? 

895. Give the characters of limestone water. 

896. What is said of sand and gravel waters ? 

897. What are the foreign ingredients of alluvial waters ? 
8^8. The impurities of surface and sub-soil waters ? 

899. What is said of marsh-water ? 

400. What is the general character of river- water ? 

401. What is said of sea-water ? 

402. How may perfectly pure water be obtained ? What water may 
be regarded as most healthy ? 

403. What is said of the organic impurities of water ? 

404. What kinds of impurities are likely to produce dyspepsia ? 

405. What kinds of water are said to produce diarrhoea ? 

406. 407. Are dysentery and cholera ever caused by impure water ? 

408. How are malarious fevers often produced ? 

409. What is the supposed cause of goitre ? 

410. What animals may pass into the body with the drinking-water? 

411. Are the senses alone trustworthy in the examination of water? 

412. What is said of distillation as a means of purification ? 

413. What is the effect of boiling and freezing ? 

414. What chemical substances are sometimes used as purifiers? 

415. What is said of filtration? 

416. How is water affected by contact with lead ? 



CHAPTER XYIl. 

417. Into what four groups may food be classed ? 

418. What is said of the proteids ? 

419. What of the fats as articles of diet ? 

. 420. What substances belong to the amyloid group ? 
T 421. To what uses are these various food-stuffs applied? 
\ 422. What are the mineral aliments? 

423. Why is a mixed diet necessary ? 

424. What is said of milk as food ? 

425. Of butter and cheese ? 

426. What is the composition of eggs, and how should they be 
cooked ? 

427. What is said of the various meats ? 

428. Why is salt inferior to iresh meat ? 

429. What peculiarity does poultry and game present ? 

430. How is the flesh of fish regarded as food ? 

431. 432. What is said of crabs and lobsters ? Clams and oysters ? 
433. Why is wheat such a yaluable food ? 



QUESTIONS. 409 

434. How does rye compare with wheat? 

435. What of buckwheat ? 

436. How does Indian com differ from wheat and rye ? 

437. What advantage does rice possess over other ibods ? 

438. What is said of peas and beans ? 

439. Give the composition of potatoes. Why should the succulent 
vegetables be eaten with meat ? 

440. What is said of the fruits ? 

441. What are auxiliary foods ? 

442. What substances come under the head of condiments ? 

443. Why is tea valuable as a beverage ? How should it be made 9 
What is its action ? How is it adulterated ? 

444. What is the composition of coffee ? How should the beverao^e 
be prepared ? ° 

445. What is said of cocoa and chocolate ? 

446. What should cooking aim to accomplish ? Why should over- 
cookmg be avoided ? 

447. How does boiling affect meat ? How should the process be con- 
ducted ? What is said of roasting ? Stewing ? Fryino- ? 

448. How should vegetables be cooked ? ^ ' 

449. What are some of the effects of over-eating? 

450. What are the effects of deficient diet ? 

451. Amount of food daily required. 

452. What results from a badly-constituted diet ? 

453. What is sai<i of a diet deficient in fat ? 

454. What constitutes unwholesome food ? 

^ 455. Give an account of the cysticercus celulosus. Of the trichina 
spiralis. 

CHAPTER XYIII. 

456. What is said of the purposes for which clothing is worn 9 

457. What of linen as an article of clothin"- ? 

458. How does cotton differ from linen ? ° * 

459. What are the properties of woollen clothing? Its relations 
to moisture ? 

460. How does color iniauence the character of clothino-9 

!!!i* )X^^^ !^ ^^ ™^^^ importance than the character of the fabric ^ 

462. W hy should clothing be light ? 

463. Why should it be worn loose ? 

f ?r* wJ'^* ^^ ^'""^ ^^ compressing the chest and abdomen ? 
4bo. What results from compressing the feet ? 
466. How is uniformity of temperature to be maintained 9 
46/. How is a part affected when habitually over-heated ? 

468. Why is over-dressing the throat pernicious ? 

469. What is said of wearing flannel next the skin 9 

470. How should children be clothed ? 

471. Why should the aged be well protected ? 

CHAPTER XIX. 

472. What renders it evident that man is intended for action ^ 

473. What IS said of labor ? What causes division of labor ? How 
does It affect the individual ? 

18 



t 




410 QUESTIONS. 

474. How does exercise remedy the evil ? 

475. Describe the transformation of physiological forces. 

476. Why is habitual exercise invigorating ? 

477. How does exercise affect the circulation ? How the tempera- 
ture ? 

478. What is its influence upon respiration ? Why should we exercise 
in pure air ? 

479. How does exercise affect digestion ? Why is immediate exercise 
after a full meal injurious ? 

480 What is tlie effect of exercise upon the skin ? 

481. How should exercise be regulated ? 

482. What are the most fkvorable conditions for exercise? 

483. Why is over-exercise injurious ? How is proper rest to be 
secured ? How should exercise be managed after sickness ? How does 
over-exercise injure the system ? Why does it particularly injure the 
young? 

484. What are the consequences of insufficient exercise ? Describe 
its operation in different circumstances. 

485. What is said of the amount and conditions of exercise ? What 
course should the sedentary pursue ? Why is pure air specially necessary 
during exercise ? 

486. What is the value of the " movement-cure " ? 



CHAPTER XX. 

487. Why is mental health a physiological question ? 

488. What is said of the office and changes of the brain ? What is 
the effect of disturbing its normal movement ? Describe the mutual rela- 
tions of the mind and brain. What is remarked as to materialism ? 

489. What constitutes disease? What error is to be guarded against ? 
How is mental disease to be regarded ? On what is Mental Hygiene 
founded ? What is its province ? What is said of diseases of the brain ? 
AVhy have all a vital interest in the subject ? 

490. Describe the modes of mental action. How are these psychical 
elements to be regarded ? In what forms may insanity manifest itself? 

491. What are hallucinations ? Examples. AVhat are illusions ? 
Examples. Delusions ? What is delusional insanity ? 

492. Describe the different phases of emotional insanity. Give the 
example of congenital perversity. How is the other class of cases affect- 
ed ? Describe the case given by Dr. Maudsley. What is said of moral 
insanity ? Repeat the remarks of Dr. Carpenter. Of Dr. Ray concern- 
ing moral endowments. What of the different elements in the moral 
faculty ? To what conclusion are we led ? 

493. What is mania ? Its kinds ? What is acute mania ? Give 
the mental differences in cases of acute mania mentioned by Bucknill and 
Tuke. Describe chronic mania. 

494. In what does monomania consist ? Mention different kinds. 
Give the case described by Dr. Bucknill. 

495. How is melancholia manifested ? Describe the victim of simple 
melancholia. What are its forms ? Relate the case mentioned by Dr. 
ConoUy. How does melancholia affect the intellect ? 

496. Define general paralysis. Who are generally its victims ? De- 



QUESTIONS. '^11 

scribe the progress of the disease. How is the accompanying mental im- 

^Tef Cwtattoel dSt^^^^^^ What are its stages? When 

ic5 it Driraarv ? When secondary ? „ . . ,. ,. 

498 What is idiocy? Describe its degrees. Ho^Y is idiocy dis- 

^^^^499! What does the term idiocy denote ? How is it manifested ? 
How do imbeciles compare with idiots ? 

500! What is said of perverted mental action that never passes mto 

"^'''501 Why are the causes of cerebral impairment varied and complex ? 
How are they usually divided ? What are predisposing causes ? Excit- 
ing causes ? What error is mentioned? In what way is msanity usu- 

^^^^5oT' What is said of each mental act ? What is the composition and 
action of the mental mechanism ? What are the results ot its perfect or 
imperfect nutrition ? Repeat the remarks of Bucknill and Take. ^^ uat 
further effect is due to impaired nutrition ? ,, , . ^ 

503 What is said of the blood transmitted to the bram ^ 

504 What are the relations between mental excitement and the 
brainward flow of blood ? Ho\v is congestion induced, and what are its 

^^^tol What is anaemia, and how caused ? What are its effects as com- 
pared with those of hypercemia ? Give Dr. Maudsley's remarks upon the 

^^ "506 What keeps the brain in harmonious action ? How may its har- 
mony be further disturbed ? Mention examples of perversion ot blood. 
How does alcohol affect the brain ? . , r .u 

507. How does the brain differ in action from other organs ot the 
body ? * How does nature renovate the brain ? What is a prime condi- 
tion of mental health ? What are the effects of insufficient sleep ? ^^ hat 
of disturbed sleep ? In what does mental health consist ? From what 
arises mental impairment ? Hence, what causes influence mental char- 

acter ? 

508. Give the estimates relative to the transmission of Insanity. What 
is transmitted, and how ? Repeat the remarks of Dr. Maudsley. 

509. How is debiUtated stock a source of criminality ? What is 
Dr. Howe's opinion upon this subject ? Name some of the causes of 
mental impairment and their operation. Give the observations of Dr. Ray. 

510. What comparison is made between the savage and the civilized 
man ? What are our peculiar perils as a nation ? 

511. What is said of overtasking the intellect? Repeat the testi- 
mony of Dr. Carpenter. What conditions control the amount of healthful 
brain-work ? How is the argument against the uuwliolosome effect of 
excessive brain-work met ? In what respect docs the brain of the savage 
and the civilized man differ ? AVhat usually works the mischief in cerebral 
application? . 

512. How is cerebral disease heralded ? How the more active torms .-' 
In what manner is the conduct affected ? The consciousness ? 

513. What hints and precautions are given? How should children 
thus predisposed be managed ? How adults ? What is Dr. Ray's advice 
when there is a predisposition to mental disease? 

514. What is said of medical management ? 



IKDEX. 



Abdomen, 23. 
Abdominal aorta, 106. 
Abduction and adduction, 166. 
Absorption, 14E<, 152. 
Accessory tood-stuffs, 189. 
Ascending colon, 149. 
Acetabulum, 165. 
Acidulous watei-s, 299. 
Action, man intended for, 344. 

" of the valves, 50. 
Active powers, 153. 
Adam's-apple, 171. 
Adjustment of the eye. 212, 215. 
Adulteration of milk, 812. 
Adulteration of vinegar, 31S. 
Aerial waves, 196. 
Aiferent nervfs, 177. 
Agencies of puritication, 291. 
Air, 21. 

" contamination of, by various trades, 
287. 

" danger of over-heating, 294. 

" heating of the, 294. 

'' inspired and expired, 88. 

" in respiration. 97. 

" in the lungs, 97. 

" as atiected by exercise, 352. 
Air-cells, 87. 
Albumen, 134, 309. 
Alcohol, effect of, 380. 
Alimentary af)])aratus 33. 

canal, 24, 108, 133. 
Alimentation, 33. 

'• daily gains of, 133. 

" ob.iect of, 139. 

Alluvial waters, 800. 
Alveoli. 143. 
Ammonia, 34, 326. 
Amoeba, 69. 

Amount oi air required for ventilation, 292. 
Amphibia, blood-corpuscles of, 71. 
Amphioxus, 70. 
Ampullae, 189. 
Amyloids, 129, 134, 308. 

" prove injurious as diet, 135. 



Anatomy, 15. 

'^ outlines of, 23. 
Animal charcoal, 807. 

foods, 812. 
Ankle-j(»int, 161. 
Anus, 151. 
Aorta, 44, 

Applied physiology, 276. 
Aqueous humor. 210. 
Arachnoid membrane and fluid, 237. 
Areolar tissue, 27. 
Arms, bones of the, 29. 
Arteries, 83, 87. 
Arteries and veins, difference between the, 

89. 
Arterial blood, 82. 
Artery, hepatic, 121. 
" venal, 114. 
" splenic, 128. 
Articulation, 159. 
Artificial reflex actions, 254. 
Arytenoid cartilages, 171. 
Asphyxia, 104. 

" causes of, 105. 

" slow, 105. 
Atlas, 162. 
Atmosphere, constitution of the, 282. 

" impuritiesof the, 283. 298. 

Atmospheric impurities, their relations to 

the senses, 283. 
Atoms, 153. 
Auditory muscles, 198. 

" nerves, 188. 195. 

" ossicles, 198. 
Auditory spectra, 222. 
Auricles, 47. 
Auriculo-ventricular ring, 50. 

" •' valves, 50. 

Auxiliary food, 818. 
Axis, 162. 

Axis, cerebro-spinal, 236. 
Axis-cylinder, 273. 
Axis, the optic, 230. 

Ball and socket-joints, 161. 



INDEX. 



413 



Basilar membrane, 190. 
Beans and peas, 317 
Beet; 313. 
. Beef-tea, 324. 
Beets, 317. 
Biceps muscle, 28. 
Bicuspid teeth, 143. 
Bile, 107, 120, 124, 151. 
Bile-duct, 120. 
Bilin, 123, 124. 
Bilioasness, 327. 
Biology, 14. 

•' divisions of, 15. 
Black clothes, 334. 

*' pepper, 319. 
Bladder, 110. 
Blind spot, 204. 
Blood, appearance of, when magnified, 65. 

" arterial and venous, 81. 

" 'arterial distribution of, 106. 

" changes of the, 83. 

" circulation of the, 34. 

" coagulation of the, 66. 

** composition of the, 77, 81. 

" corpuscles of, 66. 

" crystals of, 72. 

" flow of, through the heart, 53. 

" perversicns of, 379. 

'• poverty of, 379. 

" puriticatton of, 86. 

" quantity in the body, 79. 

" sources* of loss and gain to the, 
106, 109. 

" " thicker than water," 77. 

*' transfusion of, 80. 

" and lymph, 65. 
Blow on the head, effect of a, 81. 
Blushing, 60. 

Body, functions of tbe, 19. 
Boiling, 306, 324. 
Bone, 28. 

'• structure of, 263. 
Bony labjTinth, 192. 
Brain, 25. . 

" and mind, 353. 

" anatomy of, 246. 

"• congestion of, 378. 

" convolutions of, 248. 

" diseases of, 356. 

" hemispheres of, 248. 

" influence of, 362. 
lobes of, 248. 

" nutritive repair of, 380. 

" reflex actions of, 253. 

" seat of sensation, 32. 

" sulci of the, 248. 
use of, 388. 
Bread. 138,311. 
Breast-bone, 29. 
Brewster, Sir D., 223. 
Bright's disease, 340. 
]>roilin<z, 325. 
Bronchitis, 287. 
Bronchi, 91. 97, 100. 
Bronchial tubes, 86, 91. 
Brunner's glands, 149, 
Buccal glands, 142. 
Buckwheat, 316. 
Bufly coat, 73. 



Bunions, 839. 
Butcher's meat, 138. 
Bursal, 167. 
Butter, 312. 
Butter of cacao, 323. 

Cacao-beans, 323. 
Ca3ciim. 149. 
Cafiein,' 321. 
Camera obscura, 209. 
Canaliculi, 263. 
Canals of the ear, 100. 
Canine teeth, 143. 
Capillaries, 33, 37. 

" causes of steady flow in, 58. 

" of the lungs, 84. 

" why pulseless, 57. 

Capsular ligament, 165. 
Carbon, 184, 138. 
Carbonate of lime, 20, 28, 299. 

of soda, 3U0. 
Carbonic acid, 20, 34, 82, 133. 

'' " as an atmospheric impu- 

rity, 283. 
Carbonic acid, excretion of, 107. 

'•' *' proportion of, in surface 

soil, 299. 
Carbonic acid, quantity thrown off" by the 

lungs, 284. 
Carbonic acid, poisonous nature of, 1C4. 
Carbonated waters, 299. 
Cardiac dilatation, 145. 
Cartilage, 28, 260. 

" articular, 29. 
Caruncula lachrymalis, 217. 
Casein, 134. 309. 
Catherine wheel, 204. 
Causes of disease, 279. 
Cavities of the heart, 48. 
Cayenne pepper. 319. 
Cellars, foul air of, 287. 
Cerebellum, 247. 
Cerebral hemispheres, functions of the, 

252. 
Cerebral circulation, disturbance of, 877. 
" nerves, 249. 
" structures, nutrition of, 376. 
Cerebro-spinal axis, 25, 236. 

" " functions of the, 31. 

" system, 236. 

Cerebration, unconscious, 252. 
Chalybeate waters, 299. 
Changes of the food, 138. 
Charcoal as a deodorizer, 295. 
Charcoal-filters, 307. 
Check-ligaments, 165. 
Cheese, 312. 
Chemistry, 14. 
Chest, 24. 

'' bones of the, 29. 
Chest- walls, 92. 
Chewing, 144. 
Chloride of potassium, 310. 

'' of s«>dium, o(^0. 
Chlorine as a disinfectant, 296. 
Chocolate, 323. 
Cholera, 304. 

'■' as influenced by hygienic meas- 
ures, 279. 



414 



INDEX. 



Cholesterine, 124. 
Chondrin, 131 260. 
Chorda tendina, 50, 54. 
Choroid coat, 2i0. 
Chyle, 43. 151. 
Chyme, 149. 
Cilia, 91. 154. 

" movements of the, 154. 
Ciliary processes, 210. 
" ligament, 211. 
" muscle, 211. 
Ciliated epithelium, 253. 
Circumduction, 166. 
Circulatorr apparatus, 33. 
Circulation affected by exercise, 346. 
'" compared to a river, 81. 

" course of the, 59. 

'• evidence of, 63. 

Circum vallate papillae, 183. 
Cistern-water, 302. 
Cistern of the chyle, 43. 
Clams, 315. 
Classification, 16. 
Clothing, 332. 

" absorption of moisture by, 333. 
" children's, 341. 
" for the aged, 341. 
Clot, 73. 
Cochlea, 188, 190. 

" function of, 199, 
Cochlear nerve, 199. 
Cocoa, 323. 
Cod-liver oil, 328. 
Coffee, 321. 

adulteration of, 322. 
Cold, 182. 
Colic, 326. 
Colon, 149. 
Coior-blindness, 205. 
ColumniB cornese, 50, 54. 
Combination of actions, 29. 
Complementary colors, 205. 
Complex sensations, 219. 
Compression of the chest, 335. 

" of the feet, 333. 

Concha, 196. 
Condiments, 318. 
Conditions intiuencing the coagulation 

of the blood, 74, 
Condy's fluid. 295. 
Congestion, 62, 340, 378. 
Conjunctiva, 209, 217. 
Connective tissue, 27, 261. 
Consonants, 175. 
Constipation, 326. 
Constricting the neck, 335. 
Consumption, 283, 328. 

of oxvgen, 138. 
Controlling action of the nerves, 38. 
Control over the circulation, 60. 
" " the heart, 62. 

" " respiration, 99. 

Convex lens, 208. 
Convolutions of the brain, 248. 
Cooking. 823. 
Cornea, 209. 
Corns, 339. 

Coronary arteries and vein, 46. 
Corpora quadrigemina, 247. 



Corpora striata, 249. 
Corpus callosum, 248. 
Corpuscles of bone, 263. 

" of human blood, 266. 

" of spleen, 128. 
Costal respiration, 94. 
Cotton, 333. 
Conghing, 96. 
Crabs and lobsters, 315. 
Ciassamentum, 73. 
Cribriform plate, 186. 
Cricothyroid muscles, 162. 
Cricoid cartilage, 171. 
Crucial ligaments, 165. 
Crura cerebri, 247. 
Crystalline lens, 210, 260. 
Cutting teeth, 144. 
Cylindrical epithelium, 257. 
Cysticercus cellulosus, 330. 

Debilitated stock, 385. 
Deciduous teeth, 269. 
Deep wells, 302. 
Deficiency of fat, 328. 
Deficient diet, 326. 
Deglutition, 144. 
Delirium tremens, 223. 
Delusions, 359. 

instances of, 223-228. 
" of the judgment, 222. 

" optical, 229. 

Dementia, 369, 370. 
Dentine, 267. 
Deodorizers, 295. 
Dermis, 26. 
Descending colon, 149. 
Development. 15. 

of blood corpuscles, 69. 
Dextrine, 1^6, 135. 
Diaphragm, 24, 47, 93 • 
Diaphragmatic respiration, 94. 
Diaphragm of the eye, 211. 
Diarrhoea, 326. 

" caused by river-water, 803. 
Diastole, 52. 
Digastric muscle, 168. 
Digestion, artificial. 147. 

" how affected by exercise, 347. 

"■ second, 151. 

Disease, old notions of, unfavorable to 
hygienic efforts, 277. 
" open-air treatment of, 293. 
*' propagation of, 290. 
" true idea of, 278. 
" causes of, 279. 
Distillation, 306. 
Dorsal chamber, 24. 
Double hinge-joint, 161. 
Dressing the body, 335. 
Drinkinsr, 145. 
Drum of the ear, 193. 
Dry air, 285. 
Duct, hepatic, 121. 
Ducts of the glands, 155. 
Ductless glands, 70. 
Duodenum, 148. 
Dura mater, 237. 

Duration of light-impressions, 204. 
Durham jail, 305. 



INDEX. 



415 



Durham and Northumbeiland, colliers of, 

287. 
Dysentery, 304. 
Dyspepsia, 302, 326. 

Earthy carbonates. 318. 

Ear, 180. 

Ease in vvalkinof, 338. 

Eating, 144. 

Economy of mixed diets, 138. 

Efferent nerves, 177. 

Effgs, 313. 

Etbow-joint, 161. 

Elementary Hygiene, 273. 

Elimination of heat, 139. 

Emotion, 60, 178. 

Emphysema, 287. 

Enamel of the teeth, 267. 

Endocurdium, 49. 

Endolymph, 189, 190. 

Engorgements, 340. 

Entozoa, 305. 

Epidermis, 26, 257. 

Epiglottis, 86, 140. 

Epitiielial cells of the arteries, 38. 

Epithelium, 27, 181, 189, 257, 286. 

Erect position of man, 29. 

Essential food-stuflfs, 139. 

Etiology, 17. 

Eustachian tube, 141, 193. 

" " function of the, 200. 

Evaporation, 130. 
Excess of food, 325. 
Excretion, 33. 
Excretions, forms of, 21. 
Excretion of carbonic acid, 99, 103. 
Excrementitious matter, 21. 
Excretory f)rgans, 34, 
Exercise, 345. 

" amount and time of, 351. 

" efiect upon circulation. 346. 

*' " " digestion. 347. 

" " " respiration, 346. 

*' " " skin, 347. 

" excessive, 849. 

" mind in, 348. 

" insufficient, 349. 

'' remedial influence of, 352. 

"■ regularity of, 348. 

Exhaustion of the retina, 205. 
Expiration, 88. 
Explosive consonants, 175. 
Extension, 163. 
Extra vascular parts, 36. 
Eye, 180, 201. 
" adjustment of the, 212, 215. 
" humors of the, 210. 
Eyeball, 209. 
Eyelashes, 217. 
Eyelids, 209, 217. 

Facial nerve, 249. 

FcX^ces, 21,33. 

Fascia, 270. 

Fats. 134, 138. 308. 

Fat-cells, 262. 

Fat, pure, injurious as diet, 135. 

Fauces, 140. 

Feeling, 178. 



Feeling, loss of, 31. 
Fenestra? ovalis, 193. 

'• rotunda, 193. 
Fibrenogin, 76. 
Fibres of Corti, 189. 

'^ " function of, 199. 
Fibrillse, 271. 
Fibrin, 72, 134, 309. 
Fibro- cartilage, 100, 262. 
Fibrous tissue, 27. 
Filiform papillae, 183. 
Filters, 3U7. 
Filtration, 307. 
Fish, 814. 

Fissures of the cord, 237, 
Fissure of Svlvius, 243. 
Flatulence, 326. 
Flesh parasites, 329. 
Flexion, 166. 
Flour, 816. 
Focus, 208. 
Food, 21. 

Food and force, 23. 
Food of children, 321. 
Food-stuffs, 134. 
Foot. 29. 
Fore-arm, 163. 
Form of the boot, 339. . 
Foul air, effects of, upon the course of 

disease, 290. 
Foul air, effects of, upon inherited taints, 

290. 
Foul air, eff'ect of, upon the mind, 291. 
French troops in Mexico, 304. 
Frog, experiment with the, 63. 
Fruit, 318. 
Frying, 806, 324. 

Functions of the spinal nerves, 239. 
Fungiform papillae, 183. 

Galvanic shocks, effects of, 31. 
Gall-bladder, 121, 151. 
Game, 814. 
Ganglia, 62. 

Ganglia, sympathetic, 24. 
Ganglionic corpuscles, 272. 
Gaseous diffusion, 73. 
Gastric juice. 146. 
Gelatine, 27, 134, 262, 309. 
Glands, buccal, 142. 

'' lachrymal, 217. 

" Meibomian, 217. 

" parotid, 217. 

" of Lieberkiihn. 131, 149. 

•' submaxillary, 142. 

" sublinsrual, 142. 
Globulin, 62, 76. 
Glommerulus, 113. 
Glosso-pharvuffeal nerve, 183, 249. 
Glottis, 89, 96, 142, 1S5. 
Glucose. 120. 
Gluten, 134, 315. 
Glycosien, 120, 126. 
Glychocolic acid, 123. 
GlVchocolate of soda, 124. 
Goats' milk, 312. 
Goose-skin, 260. 

(Toitre, or Derbvshiro neck, 127, 805. 
Gout, 27S. 



416 



INDEX. 



Grassi's experiments, 293. 
Gray matter, 288. 
Grinding-teeth, 144. 
Gullet, 141. 
Gum, 126, 310. 

Hrematin, 63, 72. 
Hairs, 3(3, 259. 
Hallncinations, 357. 
Hard water, 2y9, 305. 
Haversian canals, 264. 
Head, 23. 

"• movements of the, 163, 
Hearing, 180. 

sense of, 188. 
Heart, 21, m. 

*' beating of the, 5& 

" position, 47. 

" sounds of the, 56. 

*' structure of the, 46. 

" rh.vthm of the, 52. 

" walls of the. 58. 

" working of the, 52. 
Heat, generation of, 128. 

'• producers, 189. 

" 1 eguiation of, 130. 
Hepatic circulation, 121. 
" artery, 46, 121. 

duct, 121. 
" vein, 46, 120. 
Hereditary transmission, 382. 

" cfbodily defects, 383. 
" " of insanity, 364. 

High-heeled hoots, 339. 
Hilus, 109. 
Hinge-joints. 161. 
Hip-joint, 161 
Histoloscy, 15, 255. 
Hollow muscles. 159. 
Horripilation, 26. 
Human milk, 312. 
Human body, structure of the, 23, 25. 

*• " waste and renewal of the, 22. 

Humerus, 164. 
Humors of the eye, 210. 
Hunger, 21, 826. 
Hydrochloric acid, 146. 
Hydrogen. 21, 134. 
Hygiene. 18. 
Hygienic agencies, remedial influence of, 

280. 
Hygienic knowledge, effect of> npon the 

actions, 281. 
Hygroscopic water, 334. 
Hyoid bone, 171. 

Ice-chamber experiment, 20. 

Idiocy, 871. 

Ileum, 148. 

Ileo-cfEcal valve, 149. 

Iliac arteries, 106. 

Illusions, 858. 

Imbecility, 373. 

Imperfect joints. 159. 

Impure water, effect of, upon the senses, 

306. 
Incisor teeth, 143. 
Incus, 194. 
Indian corn, 311, 316. 



Ingrowing toe-nails, 839. 
Inherited taints, 290. 
Insalivation, 144. 
Insanity, emotional. 859. 

causes of, 375, 376. 

" precautions as to, 392, 893. 
Insensible perspiration, 115, 284. 
Integument, 26. 
Intellect, aberrations of, 857. 
Interartieular cartilage, 161. 
Intercostal muscles, 92. 
Intermittently active sources of loss, 131. 
Intermittent action of the glands, 131. 
Intervertebral foramina, 238. 
Intestines, 148. 
Intestinal circulation, 150. 

" juice, 149. 
Intralobular veinlet, 122. 
Invertebrate animals, blood corpuscles o^ 

70. 
Iris, 155. 210. 
Iron, 300. 

Jaws, the, 143. 

Jejunum, 148. 

Joints, 29. 159. 

Judgments and sensations, 220. 

Jugglers, how they drink standing on 

their beads, 145. 
Jumping, 168. 

Kidneys, 24, 34, 112. 

Kidneys and lungs compared, 110. 

" medullary and cortical parts, 112. 

" shape and position of the, 109, 
113. 
Knowledge, twofold value of, 275, 

Labor, 344. 
Lachrymal gland, 217. 

-' sac, 217. 

Lacteals, 43. 152. 
Lactic acid, 141. 
lacuniK. 268. 
Lancelot, 70. 
Large intestine, 148, 152. 
Larynx, S6, 170. 
Lateral ligaments, 165. 
Lead poisoning, 301. 
Legs, bores of the, 29. 
Levator muscle of the eyelid 217. 
Levers of the bodv, 156. 
Ligaments, 29, 161, 262. 
Light, 207. 

'' sensation of, 203. 
Lisht and heavy clothing, 335. 
Lightin.q-, products of, 286. 
Limbs, 23. 
Lime-water, 20. 
Limestone-waters, 299. 
Limiting-membrane, 202. 
Linen, 332. 
Lips, 183. 
Liver, 24, 120. 

" cells, 128. 

" sugar, 125. 
Lobules of the liver, 120. 
Locomotion, 153. 
Long-sight, 215. -^ 



INDEX. 



417 



Loose clothinor, 335. 
Lower jaw, 143. 
Lungs, 24, 44. 

" amount of work done by the, 89. 
" double function of the, 34. 
" elasticity of the, 93. 
" kidneys, and skin, compared, 119. 
Lymph, 318. 

" corpuscles, 70. 
Lymphatic capillaries, 42. 
"' glands, 42. 

" system, 126. 

Macula lutea, 201. 

Magnifyinof glasses, 232. 

Malarious f<iver3, 305. 

Malleus, 193. 

Malpighian capsule, 113. 

Mammals, blood-corpuscles of the, 70. 

Man, erect position of, 29. 

Mania, 363, 364. 

Marrow, 264. 

Marsh-water, 300. 

Mastication, 144. 

Materialism, 354. 

Mathematics. 13. 

Matter, whence gained, 124. 

Meats, 313. 

Meatus, 193. 

Mechanical force, 21. 

Medical management, 394. 

Medulla oblongata, 99, 246. 

*' " decussation of fibres 

in, 251. 
Meibomian glands, 217. 
Melancholia, 365. 
Membrane of Corti, 190. 
Membranous labyrinth, functions of the, 

199. 
Mental action, modes of, 357. 

" disease, 355, 379. 

" evolutions, 31, 61. 

" health, 353. 

" hygiene, foundations of, 355 

" impairment, degrees of, 374. 

" " in what consists, 3S5. 

" over-action, evils of, 3S8. 

" under-action, 389. 
Mesenteric glands, 44. 
Mesentery, 44. 
Milk, 312, 327. 
Milk-teeth, 269. 
Mind, controlling power of the, 31. 

" in exercise, 348. 
Mineral aliments, 310. 

'' ingredients of water, 299. 
Mitral valve, 50. 
Mixed diets, 138, 311, 327. 
Modiolus, 190. 

Modulation of the voice, 174. 
Molars, 269. 
Molar-teeth, 143. 
Monomania, 3j5. 
Moral insanity, 353. 

"" perversities, 359. 

" sense, elements of, 362. 
Morphology, 15. 
Motion, 153. 
Motor nerves, 177. 

18* 



Motores oculi, 249. 
Mouth, 25, 140. 185. 
Movements of the joints, 166. 
Mucous, 27. 

'• membrane, 27. 
Muffling the throat, 340. 
Multiplying glasseo, 231. 
Muscles, 28, 154. 

" insertion of, 167. 

" of the alimentary canal, 154. 
, " of the eye, 216. 

" of the heart, 154. 

" of the lymphatic vessels, 154. 

" origin of, 167. 

" structure of, 210. 
Muscular contractility, 154. 

" fibres of the arteries, 38. 

" fibres of the heart, 49. 

" sense, 179. 

" waste, 132. 
Musical notes, 173. 

Musk-deer, blood-corpuscles of the, 71. 
Mustard, 319. 
Mutton, 313. 

Nails, 36, 258. 
Nasal cavities, 141. 

" chambers, 185. 

" passages, 86. 
Nature's standard of purity, 292. 
Negative deflection, 241. 
Nerve fibres, 272. 
Nerves, motor and sensory, 240. 

of the heart, 62. 
Nerve-tissue, structure of, 272. 
Neurilemma, 181, 273. 
Nitrogen, 21, 89, 134, 282. 
" starvation, 136. 
Nitrous acid, 296. 
Norwood school, 289. 
Nucleated cell, 69, 256. 
Nuclei, 35, 256. 
Nutrition, 32. 

" of cerebral structures, 376. 

Objects and their visual images, 230. 

Odontoid process, 162. 

CEsopha2:us, 141. 

Olfactory nerves, 1S4, 186, 249. 

Onions, 318. 

Openinsrs cf the pharynx, 141. 

Optic axis, 230. 

" nerves, 201, 203, 249. 

'• thalami, 248. 
Optical delusions, 229. 
Orbit, 201. 
Organic matter, presence of, in various 

waters, 299, 300. 
Os orbiculare, 194. 
Ossification, 2li4. 

" centres of, 266. 

Otoconia, 1SS. 
Otolithes, ISS, 195. 
Outlines of anatomy, 23. 
Overcooking, 827. 
Over-exercise, o49. 
Overtasking the brain, 8S2. 

" " emotions, 3S7. 

" " intellect, 887, SSS. 



418 



INDEX. 



Oxidation. 85, 129. 
Oxygen, 35, 89, 134, 282. 

"^ absorption of, 121. 
Oysters, 315. 

Pancreas, 24, 132, 148. 
Pancreatic juice, 151. 
Palate, 140, 183. 
Papilla?, 181. 
Paralysis, 240. 

" general, 368. 
Parkers experiments, 293. 
Parotid glands, 142. 
Parsnips, 317. 
Peas and beans, 317. 
Pectine, 318. 

Pelvis of the kidney, 112. 
Pepsin, 146. 
Peptic glands, 146. 
Peptone, 147. 
Pericardium, 47, 75, 237. 
Perilymph, 190, 195. 
Periosteum, 264. 
Peristaltic contraction, 150. 
Peritoneum, 120, 148. 
Permanent food, 135. 
Permanganate of potash, 295. 
Perspiration, 117, 231. 
Pharynx, 85, 140, 185. 
Phenomena, coexistences and sequences 

of, 12. 
Phosphorus, 134, 206. 
Phosphate of lime, 28. 
Physics, 13. 

Physiology, divisions of, 11. 
" study of, 18. ■ 

" human, 19. 

Physiological balance, 22. 
Pla-mater, 237. 
Pigment-cells, 210, 263. 
Pineal gland, 248. 
Pituitary body, 248. 
Pivot-jomt, 162. 
Plasma, 66, 72. 
Pleura, 90. 
Plexuses, 255. 

Pneumogastric nerve, 63, 250. 
Pons Varolii, 247. 
Pf^rtio dura, 24©. 
Portio mollis, 249. 
Posterior arytenoid muscles, 173. 

" nares, 185. 
Potatoes, 317. 
Potter's asthma, 287. 
Poultry, 314. 
Practical knowledge, 275. 
Production of voice, 173. 
Pronation, 164. 
Proteids, 134, 308. 
Protein, 21. 

" necessity for its supply, 136. 
Pseudoscope. 234. 
Ptyalism, 145. 
Pulmonary artery, 44. 

" consumption, 288, 290. 

" veins, 44. 
Pulse, 56. 

Punctum lachrymalc, 217. 
Purification of air, 291. 



Purification of water, 806. 
.Purkinje's figures, 207. 
Pus-celli^, 286. 
Pylorus, 146. 

Quality of voice, 174. 

Radial fibres, 202. 

Racemose glands, 132. 

Rain-water, 298. 

Range of voice, 174. 

Receptacle of the chyle, 43. 

Rectum, 150. 

Reflex action, 99, 178, 242. 

" artificial, 254. 
Regulation of the temperature, 130. 
Renal apparatus, 109, 113.' 

'" circulation, 114, 
Residual air, 97. 
Respiration, 84. 

"• atfected by exercise, 346. 

" and circulation compared, 99. 

" difi'erent in the two sexes. 95. 

" effect of, upon the circulation, 

100. 

'' in children, 103. 

" mechanism of, 86. 

Respiratory sounds, 100. 
Reparation, 33. 
Retina, 201. 

Rhythm of the heart, 52. 
Ribs, 29, 90. 
Rice, 367. 
Rickets, 327. 
River- water, 300. 
Roasting, 324. 
Rods and cones, 202. 

" " functions of the, 206. 

Rotation, 166. 
Round ligaments, 165. 
Routes of the circulation, 66. 
Running, 168. 
liye, 316. 

Salamanders, blood-corpuscles of, 71. 
Saline substances, efl'ect of, on the blood, 

65. 
Saliva, 142. 
Salivary glands, 132. 
Salts, 135. 
Salt meat, 314. 
Sand-and-gravel waters, 300, 
Sankey's experiments, 293. 
Sanitary congress, 301. 
Sarcolemma, 49, 270. 
Scala media, 188. 190. 

" tyrapani, 190. 

" vestibuli, 190. 
Scarf-skin (see Epidermis). 
Science, 11. 

Sciences, connection of, 12. 
Sclerotic, 209. 
Scrofula, 288. 
Scurvy, 280. 
Sea- water, 301. 

Sebaceous glands, 131, 116, 259. 
Secretory glands, 107. 

" " action of; 132. 

Seiaicircular canals, 190. 



INDEX. 



419 






Semilunar valves, 51. 
Sensation, 32, 178. 

" tactile, analysis of, 220. 
Sensations and judgments, 220. 
Senses, delusions of the, 222, 
Sensitive beach, 1S8. 
Sensory organs, 35. 
" neives, 177. 
Serum, 73. 
Sewage gases. 304. 
Shallow wells, 300. 
Sheath, 27. 
Short-sight, 215. 
Shoulder-joint, 161. 
Sick-room atmosphere, 289. 
Sighing, 96. 
Sight, ISO, 

Simple sensations, 219. 
Skeleton, 28. 

number of bones in, 29. 

in, 20, 26, 115,116, 119,347. 
respiratory function of, 124. 
Skull, 24. 
Sleep, insufficient, 881. 

" quality of, 382. 
Small intestine, 148. 
Smell, 180. 

" effects of a bad, 31. 

" loss of, 187. 

*' sense of, 184. 

" sensation of, 219. 
Smooth muscles, 270. 
Sneezing, 96. 
Sniffling, 96. 
Soft palate, 140. 
*' water, 298. 

" " penetrating power, 298. 
Solvent power of water, 296. 
Sound, 196. 

Speaking-machines, 174. 
Speech, 174. 
Sphincter, 110, 160. 
&pinal accessory nerves, 250. 

" canal, 24. 

" column, bones of the, 29. 

" cord, 24, 237. 

" " conducting power of, 244. 

" ** properties of, 242, 244. 

** " injuries to the, 31. 

" nerves, 237. 

" " anterior roots of, 239 

" " functions of, 289. 

" " posterior roots of, 239, 

Spleen, 24, 127, 180. 
Splenic artery, 128. 

'^ vein, 128. 
Spongy bones, 187. 
Squinting, 234. 
Stapedius, 195. 
Stapes, 193. 
Starch, 126, 135, 310. 

" cells, 286. 
Starvation, 326. 
States of consciousness, 178. 
Stationary air, 97. 

" " composition of, 98. 

Stereoscope, 238. 
Stewinsr, 324. 
Stimulus, 17a 



Stomach, 145. 

" cardiac aperture o^ 145. 
Stretched membranes, 196. 
Structure of the kidneys, 112. 
Striated muscles, 270. 
Subjected sensations, 222, 178. 
Sublingual glands, 142. 
Submaxillary glands, 142. 
Subsoil water, 300. 
Substance, loss of, 21. 
Sugar, 135, 310. 
Sulci, 248. 

Sulphate of lime, 299. 
Sulphur, 134. 

" waters, 299. 
Sulphurous acid, 296. 
Sulphuretted hydrogen, 304, 
Supination, 164. 
Supplemental air, 97. 
Supra-renal capsules, 127. 
Surface-water, 300. 
Suspensory ligament, 210. 
Sutures, 266. 
Swallowing, 144. 
Sweat-glands, 116, 131. 
" quantity of, 115. 
Sweet-bread, 24. 
Sympathetic nervous system, 24. 

" system, 236, 255. 

Synovia, 29, 160. 
Synovial membranes, 29. 
Syntonin, 134, 3U9, 
Systole, 82. 

Tactile corpuscles, 181, 274. 

" sensibility, 182. 
Tannic acid, 319. 
Taurocholic acid, 123. 
Tape- worm. 330. 
Taste, sense of, 183. 
Tea, 319. 

" making of, 320. 

" adulteration of, 320. 
Tears, 218. 
Teeth, 36, 140, 143. 

" cement of, 267. 

" crowns of tho 143. 

" dentine of, 267. 

" development of, 268. 

" enamel of, 267. 

" fangsof the, 143. 

" structure of, 266. 

" pulp cavity of, 266. 
Temperature, effect of, on the blood, 74. 
Temporal bone, 1S3. 
Tendons, 167, 262. 
Tensor tvmpani, 195. 
Thaumotrope, 233. 
Thein, 319. 
Theobromin, 323. 
Thirst, 21. 
Thoracic duct, 42. 
Thorax, 23, 38, 94, 96. 
Thoughts, 178. 
Thymous glands;, 127. 
Thyroid cartilage, 171. 

*'' '• " action of. 173. 

Thj-roid gbnd, 1*27. 
Thyro-arytenoid muscles, 173. 



420 



INDEX. 



Tidal air, 97. 

Tight boots and shoes, 838. 

Tight clcthing, 335. 

Tissues, 27. 

Tissue f»)rmers, 139. 

Tongue, 140. 

'-' mucous membrane of, 1S3. 

" papilltE (;f, 183. 
Tongueless speech, 176. 
Tonsils, 140. 
Touch, sense of, 150. 
Tra(!hea, SQ. 
Transiormations of physiologiciil forces, 

345. 
Transmission of vibration?, 197. 
Transmissions of impressions, 241. 
Transudation, 116. 
Transverse colon, 149. 
Trapezium, 162. 
Trlcliina spiralis, 331. 
Tricuspid valve, 50. 
Trigeminal nerves, 249. 
Trunk, 23. 

Tubercular consumption, 288. 
Tuning-fork, 199. 
Turblnal bones, 187, 
Turnips, 317. 
Tympanum, 193. 
Tympanic membrane, 193. 

'' muscles, function of the, 200. 

Ulna, 164. 

Uneconomical food, 136. 
Uniformity of body, 239. 
Unproductive labor, 137. 
Unwholesome food, 324. 
Urea, 21, 34. 
Ureters. 109. 
Urethra. 109. 
Uric acid, 111. 
Urinary excretion, 110. 
" products, 380. 
Urine, constituents of. 111. 

" daily qucmtity of. 111. 

" specific gravity of, 111. 
Uvula, 140. 

Valve, ileo-caecal, 149. 
Valves of the arteries, 41. 

" " *' lymphatics, 42. 

" " " veins, 40. 
ValvulcB conniventes, 150. 
Vapor of the body, 20. 
Vascular system,'^35, 
Vaso motor nerves, 62. 
Vegetable foods. 315. 
Veins, 23, 37, 39. 
Vena cava, 44, 46, 121. 

" portje, 46. 121, 125. 
Venous blood, 81. 
" pulse, 102. 
Ventilation, 106, 292. 



Ventilation, conditions of, 292, 295. 
*■' etfects of, in mines, 293. 

'• " '• upon the sicV, 298, 

" movement of air in, 294. 

Ventral chamber, 24. 

Ventricle, 48. 

Ventricles of the brain, 248. 

Ventriloquism, 228. 

Vermifcrm appendix, 149. 

Vertebral column, 24, 160. 

Vertebrae, 24. 

Vertebrate animals, blood-corpnscles of, 
70. 

Vestibule, 169, 192. 

Vestibular sac, 19<). 

Vibrations of the tympanum, 197. 

Villi, 44, 151. 

Vinegar, 318. 

Visual images, inversion of, 280, 

Visual size and form, 232. 

Vital eddy. 153. 

Vital food-stuffs, 135. 

Vitreous humor, 202, 210. 

Vocal chords, 86, 170. 
'' cushions, 171. 

Voice, 170. 

Volition, 178. 

Vowel sounds, 174 

Walking, 168. 

Walls of the heart, 49. 

Warmth, 182. 

Waste of the muscles, 132. 

" pipes, 302. 
Water, 21, 135. 

" action of, in the organism, 29T. 

" amount daily taken, 297. 

" and health, 296. 

" camera, 209. 

" excretion of, 119. 

" of interposition. 834. 

" poisoning, by lead, 307. 

" proportion in the several tissues, 
296. ' 

" punty of, 298, 301. 
Watery vapor, 20. 282, 284. 
Wearing flannel, 340. 
Weight, gain of, 22. 
"" loss of, 22. 
Wheat, 315. 
White clothes, 334. 
Will, the. 357. 
Windpipe, 86, 172. 
Wisdom-teeth, 270. 
Woollen. 833. 
Work and waste, 20, 83. 
Working of the arteries, 55. 
Wrist, 163.. 

Yellow-spot, 201. 

Zein, 317. 



B. APPLETON & CO.'S PUBLICATIONS. 



THE PHYSIOLOGY 



PATHOLOGY OF THE MIND. 

By henry MAUDSLEY, M. D., London. 
1 volume, 8vo. Cloth. Price, $4.00. 



CONTENTS : 

Part I.— Tlie Pliysiolog^y of tlte Mind* 

Chapter 1. On the Method of the Study of the Mind. 

" 2. The Mind and the Nervous System. 

" 3. The Spinal Cord, or Tertiary Nervous Centres ; or, Nervons Cen- 
tres of Reflex Action. 

" 4. Secondary Nervous Centres; or Sensory Ganglia; Sensorium 
Commune. 

" 5. Heraisphericdl Ganglia ; Cortical Cells of the Cerebral Hemi- 
spheres : Ideational Nervous Centres ; Primary Nervous 
Centres; Intellectorium Commune. 

*' 6. The Emotions. 

" 7. Yolition. 

" 8. Motor Nervous Centres, or Motorium Commune and Actuation or 
ElFection. 

" 9. Memory and Imagination. 

Part IS.— Tlie Pathology of tlie Mind. 



Chap. 1. On the Causes of Insanity. 
" 2. On the Insanity of Early Life. 
" 3. On the Yarieties of Insanity. 
Chapter 7. On the 



Chap. 4. On the Pathology of Insanity. 
5. On the Diagnosis of Insanity. 
G. On the Prognosis of Insanity. 
Treatment of Insanity. 



'' The first part of this work may be considered as embodying the 
most advanced expression of the new school in physiological psy- 
chology, which has arisen in Europe, and of which Bain, Spencer, 
Leycoch, and Carpenter, are the more eminent English representa- 
tives." — Home Journal. 

"The author has professionally studied all the varieties of insan- 
ity, and the seven chapters he devotes to the subject are invaluable 
to the physician, and full of important suggestions to the metaphy- 
sician." — Boston Transcript. 

" in the recital of the causes of insanity, as found in peculiarities 
. of civilization, of religion, of age, sex, condition, and particularly in 
the engrossing pursuit of wealth, this calm, sciontilic work has the 
solemnity of a hundred sermons ; and after going down into this ex- 
ploration of the mysteries of our being, we shall come up into active 
life again chastened, thoughtful, and feeling, perhaps, as we never felt 
before, how fearfully and wonderfully we are made." — Evening Gazette 



D, A PPL ETON & CO:S PUBLICATIONS, 



TBE PHYSIOLOGY OF MAN ; 

DESIGNED TO 

EEPRESEl^ THE EXISTmG STATE OF PHYSIOLOGICAL SCIENCE, 
AS APPLIED TO THE FUNCTIONS OF THE HUMAN BODY. 

Bjr .A^TISTIlSr iriL,i:N-T, Jr., M!. ID. 

Alimentation; Digestion; Absorption; Lymph and Chyle. 
1 volume, 8vo. Cloth. Price, $4.50. 



THE FIRST VOLUME OF THE SERIES 

BY 

.^TJSTi]>^ :b^x.iis"t, Jr., ]m:. r)., 

CONTAINING 

Introduction; The Blood; The Oironlation; Eespiration. 
1 volume, 8vo. Cloth. Price, $4.50. 



" Professor Flint is engaged in the preparation of an extended 
work on human physiology, in which he professes to consider all the 
subjects usually regarded as belonging to that department of phys- 
ical science. The work will be divided into separate and distinct 
parts, but the several volumes in which it is to be published will form 
a connected series." — Providence Journal. 

It is free from technicalities and purely professional terms, and 
instead of only being adapted to the use of the medical faculty, 
will be found of interest to the general reader who desires clear 
and concise information on the subject of man physical." — Evening 
Post 

" Digestion is too little understood, indigestion too extens^ively 
suffered, to render this a work of supererogation. Stomachs will have 
their revenge, sooner or later, if Nature's laws are infringed upon 
through ignorance or stubbornness, and it is well that all should un- 
derstand how the penalty for *high living' is assessed." — Chicago 
Evening Journal. 

" A year has elapsed since Dr. Flint published the first part of 
his great work upon human physiology. It was an admirable treatise 
— distinct in itself^ — exhausting the special subjects upon which it 
treated. " — Philadelphia Inquirer. 



Works publislied by D, Appleton & Co, 



A NEW 

CLASS-BOOK OF CHEMISTRY. 

BY EDWAKD L. TOUMAKS, M. D. 
460 Pages. 910 Engravingrs. Price $1 75. 

THe Class-Book of Chemistry, pnblislieTi some ten years ago, has been re-vmtten, re 
illustrated, and much enlarged, and now appears as an essentially new work. Its aim 
is to present the most important facts and principles of the science in their latest as- 
pects, and in euch a manner as shall be suitable for purposes of general education. This 
volume bimgs up the science to the present date, incorporating the new discoveries, the 
porrected views, and more comprehensive principles which have resulted from recent 
Inquiry. Among these may be mentioned the newly -received doctrines of the nature 
of Heat, the interesting views of the Correlation and Conservation of Forces, the dis- 
coveries in Spectrum Analysis, and the new and remarkable researches on the artificial 
production of organic substances, and on the crystalloid and colloid conditions of mat 
ter, with many other results of recent investigations not found in contemporary text- 
books. 

For philosophical accuracy of arrangement, clearness of statement, and felicity of il- 
lustration, the Class-Book is unsurpassed. — A^. Y. Teacher, 

Prof. Youmans possesses a rare faculty for bringing the intricacies of science right 
within the comprehension of the masses of readers, and his book presents all the in- 
terest of a novel. — Boston Post, 

The most recondite topics are placed in a transparent light before the common mind, 
the language is eminently choice and attractive, not an unwieldy paragraph, scarcely a 
superfluous word can be found from the beginning to the end of the work, and, in spite 
of the extreme economy of expression, there is no apparent constraint or formality, but 
every page flows smoothly and gracet\illy along, presenting a rare model of luci'd and 
agreeable didactic statement.— iV". Y. Tribune. 

The chapters on the Mutual Relations of the Forces, and on the Dynamics of Vege- 
table Growth, are alone worth the price of the volume. — B. F. Leggett^ Prof, ^at. 
Science^ Whitewater College^ Ind. 

The present volume exhibits plentiful traits of what we believe we have before 
called Prof. Youmans' educational genius. — Methodist Quarterly Eevieic. 

Unrivalled as a practical treatise. Its introduction on the " Origin and Nature of 
Scientific Knowledge" should be read by every teacher. — 2Iass. Teacher. 

One of its peculiar merits is that it can all be taught. — Prof. Phelps^ 2r. J. Xor- 
mal School. 

Clear, accurate, recent, and imbued with the enthusiasm of its author. — P. M. Jfan- 
ley, Pres. N. II. Fern. College. 

It is eminently terse and compact, is amply and lucidly illustrated, and few cf our 
many class-books that have crossed the ocean and been welcomed in Europe, are calcu- 
lated to do us more credit than this admirable work, — A^. Y. Independent. 

A thorough perusal of the bo«k enables us to pronounce it the best elementary 
chemistry that has been written in our langunge. It is penetwted by a fearless yet diei- 
ciplined scientitic spirit, and is completely up" to the level of the latest discoveries in 
the science of which it treats. We have read it with all the interest usually given to 
romance. — New Nation. 

This manual is distinguished from most other Class-books in setting almost wholly 
aside what is merely technical and experimental, for the sake of the complotost possible 
exhibition of the principles of the subject. For the thorough student, and even for the 
general reader, a c:iret\il, lucid, and connected exposition of the new views was needed, 
such as wo ai-e glad to acknowledge in the present vohnno. The auth«.T has given an 
intellectual value to his treatise very much abovt; the standiu-d aimed at in similar 
^ork s. — Christia n AU-a m in £»\ 



D. APPLET ON db CO. S PUBLICATIONS. 



Chemical Atlas : 

Or, the Chemistry of Famihar Objects. Exhibiting the General Princi- 
ples of the Science in a Series of Beautifully Colored Diagrams, 
and accompanied by Explanatory Essays, embracing the latest 
views of the subject illustrated. Designed for the use of Students 
in all Schools where Chemistry is taught. By EDWARD L. 
YOUMANS. Large Quarto, 105 pages. 

The Atlas is a reproduction (in book form), and a continuation of the 
mode of exhibiting chemical facts and phenomena adopted in the author's 
'* Chemical Chart." The application of the diagrams is here much extended, 
occupying thirteen plates, printed in sixteen colors, and accompanied by 
100 quarto pages of beautifully printed explanatory letter-press. It is a 
Chart in a portable and convenient form, containing many of the latest 
views of the science which are not found in the text-books. It is designed 
as an additional aid to teachers and pupils, to be used in connection with 
the author's " Class-Book," or as a review, and for individuals who are 
studying alone. 

It is intended to accompany the author's Class-Book of Chemistry, but 
it may be employed with convenience and advantage in connection with any 
of the school text-books on the subject. 

Prom the Home Journal. 

"Here we have science in pictures — Chemistry in diagrams — eye- dissections of all 
the common forms of matter around us ; the chemical composition and properties of 
all familiar objects illustrated to the most impressible of our senses by the aid of colors. 
This is a beautiful book, and as useful as it is beautiful. Mr. Youmans has hit upon a 
happy method of simplifying and bringing out the profoundest abstractions of science, 
so that they fall within the clear comprehension of children."" 

From the TJtica Morning Herald. 
"An excellent idea, well carried out. The style is lucid and happy, the definitions 
concise and clear, and the illustrations felicitous and appropriate." 

From the Lawrence Sentinel. 
""We have devoted some little time in looking over this Atlas, and comparing its 
relative merits with similar treatises heretofore published, and feel bound to accord to 
it the highest degree of approbation and favor." 

From Life Tllusirated. 

** This method of using the eye in education, though not the royal road to knowledge, 
Is really the people's railroad — a means of saving both time and labor. This work is 
worth for actual instruction in common schools far more than a set of apparatus, which 
the teacher might not be able to use, while every one can teach from the Atlas. We 
pronounce it, without exception, the best popular work on Chemistry in the English 
Imguage." 

From the IsTew Yorh Tribune. 

"Mr. Youmans is not a mere routine teacher of his favorite science* he has hit 
upon novel and effective methods for the illustration of its princij les. In his writings, 
as well as his lectures, he is distingui&hed for the comprehensive order of his state- 
ments, his symmetrical arrangement of scientific facts, and the happy manner in which 
he addresses the intell'ict through the medium of ocular demonstration. In this last 
respect, his method is both original and singularly ingenious." 



D. AFFLETON & C0:8 FUBLICATIONB, 

Chemical Chart. 

By EDWARD L. YOUMANS, M. D. On rollers, 5 feet by 6 in size 

New Edition. 

This popular work accomplishes for tne first time, for Chemistry, what 
maps and charts have for geography, geology, and astronomy, by presenting 
a new and valuable mode of illustration. Its plan is to represent chemical 
composition to the eye by colored diagrams, so that numerous facts of pro- 
portion, structure, and relation, which are the most difficult in the science, 
are presented to the mind through the medium of the eye, and may thus 
be easily acquired and long retained. The want of such a chart has long 
been felt by the thoughtful teacher, and no other scientific publication that 
has ever emanated from the American press has met with the universal 
favor that has been accorded to this Chart. In the language of a distin- 
guished chemist, *'Its appearance marks an era in the progress of the 
popularization of Chemistry." 

It illustrates the nature of elements, compounds, affinity, definite and 
multiple proportions, acids, bases, salts, the salt-radical theory, double de- 
composition, deoxidation, combustion and illumination, isomerism, com- 
pound radicals, and the composition of the proximate principles of food. 
It covers the whole field of Agricultural Chemistry, and is invaluable as an 
aid to public lecturers, to teachers in class-room recitation, and for reference 
in the family. The mode of using it is explained in the class-book. 

From the late Horace Mann, President of Antioch College. 
^ 1 think Mr. Youmans is entitled to great credit for the preparation of his Chart, 
because its use will not only facilitate acquisition, but, what is of far greater import- 
ance, will increase the exactness and precision of the iitudenfs elementary ideas." 

From Dr. John W. Draper, Pro/<3.ssoy of Chemistry in the University of y. Y. 
" Mr. Youmans' Chart seems to me well adapted to communicate to beginners a 
knowledge of the definite combinations of chemical substances, and as a preliminary 
to the use of symbols, to aid them very much in the recollection of the examples it 
contains. It deserves to be introduced into the schools." 

"Wo cordially subscribe to the opinion of Professor Draper concerning the vaiaa 
lo beginners of INIr. Youmans"' Chemical Chart. 

John Tokiiey, Prof, of Chemistry in the College of Physiicians d' Surg. X. Y. 

Wm. II. Ellet, Idte Professor of Chemistrtj in. Columbia College, S. C. 

James B. IIogehs, Professor of Chemistry in the University of Pennsylvania.^ 

From Benjamin Silliman. LL.D. Professor ofCliemistry in Yale College, 
' I have hastily examined Mr. Youmans"' new Chemical Diagrams or Chart of 
ctiemical combinations by the union of the elements in atomic proportions, Tho dcsigi 
appears to bo an excellent one."" 



D, AFPLETON & UU:jS PUBLICATION'S, 

The Hand-Book of Household Science. 

A Popular Account of Heat, Light, Air, Aliment, and Cleansing, m 
Iheir Scientific Principles and Domestic Applications. By E. L. 
YOmiANS, M.D. 12mo, lUustrated, 470 pages. 

Various books have been prepared which cross the field of domestic 
science at different points, but this is the first work that traverses and 
occupies the whole ground. Hardly a page can be opened to that does not 
convey information interesting and valuable to every person who dwells in a 
house. The work will be found not only of high practical utility, but capti- 
vating to the student, and unequalled in the interest of its recitations. 

From the Superintendent of Public Instruction in the State of PennsyJ/cania, 
*' The daily and hourly importance of the topics embraced in the work, their im- 
perious claims upon public attention, and their intimate connection with individual 
and social welfare, together with the compendious arrangement and copious fulness of 
information presented, and the cautious accuracy and precision of statement, make it a 
publication of the highest practical value for both the household and the school. 

" Very respectfully yours, 
"Prof. Edward L. Toumans. HENET C. HICKOK." 

From the Superintendent of Schools of the State of New York. 
"It embodies scientific information of the highest importance, arranged with much 
care, and so clearly stated that even the ordinary mind can scarcely fail to grasp and 
retain the truths it unfolds and illustrates. It would prove a most valuable class-book 
in our high schools, and I am satisfied that an examination into its merits would result 
in its general introduction into such institutions. Very respectfully yours, 

"H. II. VAN DYCK, Superintendent Public Instruction." 

From ihe Springfield Republican. 
" It is the work of a man thoroughly scientific and thorougly practical. It is no 
extravagance to say that a mastery o"f its contents will secure a better knowledge of 
the applications of Chemistry, Physiology, and Natural Philosophy, to life and life's 
concerns, than the combined treatises upon these subjects which are usually found in 
our school-rooms." 

From the Detroit Advertiser. 
" This is one of the most valuable and important books that has of late been issued 
from the press. It will do more to elevate and connect the ordinary duties of house- 
hold life with the domain of science than any other work yet published. It is so ar- 
ranged that the general reader and the man of science may refer to it with satisfaction ; 
but it is also a book which ought by all means to be introduced in our schools, and 
which every young woman who expects to be any thing more than a doll or parlor 
»utomaton,*should study and become as familiar with as she is with her prayer-book." 

From the Philadelphia Saturday Courier. 
"Few persons realize — few persons begin to realize — the importance of thoroughly 
imderstandinff the nature and elfects of light, heat, air, and food ; yet the value of such 
knowledge can hardly be overstated. Mr. Youmans' work is the clearest and fullest 
exposition of science in those relations that has yet appeared. School committees and 
persons directly interested in education, who have long been searching for a work of 
this kind, will rejoice to find the fruit of their quest in this manual. It is a valuable 
book, written for a valuable purpose : the desire to lift our ordinary domestic life int« 
inw dignity of intelligence pervades it throushout, and tinctures it in the grain," 



D. AFFLETON d- CO:S PUBLICATIONS, 
THE 

Correlation and Conservation of Forces. 

WITH AN 

INTEODUGTION AND BEIEF BIOGEAPHICAL NOTICES, 
By EDWARD L. YOUMANS, M.D. 12mo, 490 pages. 



CONTENTS. 
L By W. R. Groye. The Correlation of Physical Forces. 
II. By Prof. Helmholtz. The Interaction of Natural Forces. 
m. By J. R. Mayer. 1. Remarks on the Forces of Inorganic Nature. 

2. On Celestial Dynamics. 

3. On the Mechanical EquiYalent of Heat. 

lY. By Dr. Faraday. Some Thoughts on the Conservation of Forces. 
Y. By Prof. Liebig. The Connection and Equivalence of Forces. 
YI. By Dr. Carpenter. The Correlation of the Physical and Yital Forces. 

" This work is a very welcome addition to our scientific literature, and will b© 
particularly acceptable to those who wish to obtain a popular, but at the same time 
precise and clear view of what Faraday justly calls the highest law in physical science, 
the principle of the conservation of force. Suflicient attention has not been paid to the 
publication of collected monographs or memoirs upon special subjects. Dr. Youmans' 
work exhibits the value of such collections in a very striking manner, and we earnestly 
hope his excellent example may be followed in other branches of science." — American 
Journal of Science. 

" It was a happy thought which suggested the publication of this volume. The 
question is often asked, and not so easily answered, What are the new doctrines of the 
Correlation and Conservation of Forces? In this volume we have the answer, and 
with the reasons of its chief expounders ; those who are ignorant on that theme, can 
thus question the original authorities." — Xeio Englander. 

"We here have the original expositioTjs of the new Philosophy of Forces, accompa- 
nied by an excellent exposition of both the exposit\3ns and the expositors; the whole 
will be a rare treat to the lovers of advancing scientific thought." — JTethodiet 
Quarterly/ Review. 

"This is, perhaps, the most remarkable book of the age. We have here the latest 
discoveries, and the highest results of thought concerning the nature, laws, and con- 
nections of the forces of the universe. No higher or more sublime problem can engag* 
the intellect of man than is discussed by these doctors of science intent alone on arriv- 
lag at the truth." — Detroit Free Press. 

"■[^his work presents a praiseworthy specimen of complete and foithfiil authorship, 
and ite. publication at this time will form an epoch in the experience of many thinking 
mindd."— ib^me. 



D. AFPLETON & CO:S PUBLICATION'S. 



Class-Book of Physiology. 

By B. N. Comings, M. D., Professor of Physiology, Chemistry, and 
Natural History, in Connecticut State Normal School. 12mo. 324 



Revised Edition^ with an Appendix. 

Professor Comings' thorough acquaintance with every department of 
Physiology, and his long experience as a teacher of that science, quaUfy 
him in an eminent degree for preparing an accurate and useful text-book on 
the subject. He has lost no opportunity of introducing practical instructions 
in the principles of hygiene, thus not only making the pupil acquainted with 
the wonderous workmanship of his own frame, but showing him how to 
preserve it in a sound and healthy state. Avoiding technical terms, as far 
as possible, he has brought the subject fully within the comprehension of 
the young, and has clothed it with unusual interest, by judicious references 
to the comparative physiology of the inferior animals. Pictorial illustrations 
have been freely introduced, wherever it was thought they could aid or interest 
the student. 

Physiology cannot but be considered, by every intelligent and reflecting 
mind, an exceedingly interesting and necessary study. It makes us ac- 
quainted with the structure and uses of the organs of life, and the laws by 
which we may keep them active and vigorous for the longest period. The 
publishers would respectfully urge its importance on such teachers as have 
not heretofore made it a regular branch in their institutions ; and would 
solicit, at the hands of all, an impartial examination of what is pronounced 
by good judges, "the best elementary text-book " on the science. 

From ;M. Y. Beown, Prineipal of Webster School^ New Haven. 
" I have used Comings' Class-Book of Physiology for nearly two school terms in the 
First Department of my school. I am happy to say that I regard it the hest text-hook 
on this important branch witli which I have any acquaintance. The subjects are system- 
atically an*anged; the principles, facts, and illustrations, are clearly represented to the 
pupil. 1 find that his introduction of Comparativa Anatomy and Physics tends greatly 
to increase the interest of the pupil in this most important &nd necessary study. 1 
therefore can cheerfully recommend this admirable work to my fellow-teachers as one 
of rare excellence, and hope it may take the rank it deserves as a text-book upon this 
subject." 

From Abraham Powelson, Jk., Teacher^ Brooklyn^ New York. 
** After a very careful examination of the Class-Book of Physiology by Comings, I 
ein freely say that I consider it a performance of superior excellence. It embodies a 
fund of information surpassing in importance and variety that of any other work of tlii 
kind which has come under my notice," 



Lb re '10 



